The Digestive System

The digestive system is the system in which the human body digests food into usable sources of energy and absorbs important nutrients. Digestion begins in the mouth and ends when feces exits the body through the anus. But what occurs in between the start and the end of digestion is the process that allows humans to take in the necessary nutrients that allow them to thrive.

The Passage of Food through the Body

The alimentary canal, or gastrointestinal tract, are the names given to foods passageway through the human body. Food enters the body through the oral cavity, where it will be masticated by the teeth, while being continuously moved by the tongue. After having been properly masticated, the bolus, or the mass of food prepared by the mouth, is swallowed in a process called deglutition. There are two phases of deglutition. The first one is the voluntary buccal phase, in which the tongue forces the bolus into the pharynx. Once this has occurred,the involuntary pharyngeal-esophageal phase begins. This phase is when the bolus moves through the pharynx and the esophagus through peristalsis, which is a series of wave-like contractions through the alimentary canal.
Human_Digestive_Tract.gifOnce the bolus has moved down the esophagus, it passes through the cardio-esophageal sphincter and into the stomach, where it is churned by the mass movements of the stomach and digested by the various enzymes of the stomach. The food products in the stomach will eventually become processed to the point where it is almost liquid, at which point it is referred to as chyme. It is in this state that the chyme will move through the pyloric sphincter into the first part of the small intestine, the duodenum. Peristalsis and segmentation are the methods in which the body moves food substances through the body, and throughout the small intestine, segmentation is used. The chyme will move throughout the three parts of the small intestine, the duodenum, the jejunum, and the ileum, in this manner. The remainder of the food products will them move into the large intestine through the ileocecal valve. The first part of the large intestine is the cecum, which is connected to the vermiform appendix. After the cecum, there is the ascending colon, which leads to the transverse colon, the descending colon, the sigmoid colon and eventually, into the rectum. From the rectum the now fecal matter moves into the anal canal, which has an external voluntary sphincter and an internal involuntary sphincter. Because part of the defecation process is voluntary, people may choose when they defecate, to a certain extent.

Digestion in each Alimentary Canal Organ

Mouth: The actual chemical digestion of food begins in the mouth, with the aid of the salivary glands. The parotid, sublingual and submandibular glands all create saliva, which amongst other things, contains salivary amylase, an enzyme that begins the digestion of carbohydrates.
Stomach: The stomach contains gastric juices, which contains hydrochloric acid. The hydrochloric acid within the gastric juices activates pepsinogen, creating the enzyme pepsin which begins the digestion of protein. Other food products are also mechanically broken down in the stomach by it's mass movements, although no nutrients are absorbed in the stomach.

Small Intestine: Digestion and absorption mostly occurs in the small intestine. The enzymes that digest food substances in the small intestine come from the pancreas, as well as bile from the liver. Carbohydrates and proteins finish being digested by pancreatic amylase and trypsin, respectively. Fats, on the other hand, are completely digested in the small intestine. Fats are digested by pancreatic lipase, from the pancreas, and bile, from the liver. The products of food digestion are absorbed in the small intestine. Most of these substances are absorbed by active transport, which is when they are absorbed through the intestinal cell plasma membranes. From there, they enter the villi, and via the hepatic portal vein, enter the blood stream or liver. This said, fats are absorbed through diffusion. This is when after the substances enter the villi, they are carried to the liver by blood and lymphatic fluids.

Large Intestine: The large intestines main role in the digestive process is the absorption of water and some vitamins and ions, such as vitamins K and B. The large intestine leaves only the necessary amount of water for the fecal matter to pass smoothly, absorbing the rest.

The Breakdown of Food

Carbohydrates: The main product created by the breakdown of carbohydrates is glucose. Glucose is used to make ATP, by a process known as cellular respiration. In some cases however, when ATP is not needed, glucose can be stored as glycagon or fat, and then later broken down into glucose.

Proteins: Proteins are broken down into amino acids, which are generally used to build up functional proteins (enzymes, antibodies, hemoglobin) and structural proteins (connective tissue, muscle proteins). When there is an overabundance of amino acids, they can be used to create ATP, although this is rare.

Fats: When fats are broken down, they become fatty acids and glycerol, which once metabolized by the liver into acetic acid, can be used either to create ATP, or build myelin sheaths and cell membranes. When the fats are not needed to create any of the previously listed items, they are used to create insulation and fat cushions around the body's organs.


The Importance of Accessory Organs

Organs that are not directly a part of the alimentary canal are called accessory organs, these include the salivary glands, teeth, pancreas, the liver and the gallbladder.

Salivary Glands: The salivary glands are the first part of carbohydrate digestion. They also allow the food to create a bollus, making the process of deglutition easier as the food stays together for the most part.

Teeth: The purpose of the teeth is well known. They are the first part of mechanical digestion, mastication. By grinding the food and creating smaller fragments, saliva can reach all parts of it more easily and swallowing is facilitated by the smaller bites.

Pancreas: The pancreas produces many of the necessary enzymes for food digestion in the small intestine. The enzymes that are created there are brought to the duodenum of the small intestine, where they can be used in the digestive process. The pancreas also produces insulin and glucagon, two enzymes that are necessary in maintaining homeostasis of the blood glucose levels.

Liver and Gallbladder: The liver produces bile, which enters the small intestine through the common hepatic duct, and then through the bile duct. Bile contains bile salts, bile pigments, cholesterol, phospholipids, and electrolytes, although only the bile salts and the phospholipids aid in the digestive process. Bile salts emulsify fats. The gallbladder on the other hand stores bile when it is not being used in digestion.

liver-diagram.jpg The bile goes into the gallbladder through the cystic duct, while it can get into the small intestine through the common hepatic duct and the bile duct.

Disorders of the Digestive System

Gallstones: Gallstones occur when the bile is stored in the gallbladder for too long. When it remains there for a lengthy period of time, the cholesterol in it begins to crystallize, forming the stones.

Heart Burn: This occurs when the cardioesophageal sphincter fails to close tightly, allowing gastric juices to go into the esophagus, causing pain. Over time, this can lead to ulcers of the esophagus and is often caused by a hiatal hernia, a deformity in the stomach.

Ulcers: Ulcers occur when gastric juices erode the stomach's (and sometimes the lower esophagus' and duodenum's) mucosa. This causes painful, crater-like spots of erosion.
Diverticulitis: This is the formation of diverticula, when the mucosa protrudes through the colon wall. This occurs when the diet lacks bulk and the colon narrows, making its muscles contract more powerfully.

Diarrhea/Constipation: Diarrhea occurs when food passes too quickly through the large intestine, not allowing enough water to be absorbed. This can result in dehydration and electrolyte imbalances because the large intestine cannot absorb them. Constipation of the other hand, occurs when food remains in the large intestine for too long, and becomes hard and difficult to pass.

Lactose Intolerance: Lactose intolerance is the inability to digest lactose, the sugar found in milk. This can cause bloating, cramps, diarrhea, and nausea when dairy products are ingested.

Crohn's Disease: Crohn's disease is a form of inflammatory bowel disease in which the immune system continuously attacks the intestinal tissue, giving it thick walls. Crohn's disease can affect any part of the digestive tract, leaving some areas healthy, and others inflamed. This can cause weight loss, painful stools, diarrhea, ulcers, bloody stools, amongst other things. Crohn's disease is caused by genetic and environmental factors. These include an overreaction to a normal bacteria, a family history of Crohn's, Jewish ancestry, and smoking.
slide06.gifThis chart describes treatment methods for Crohn's Disease

Building Molecules

The molecules broken down from carbohydrates, proteins and fats are used in many different ways within the body, as demonstrated above. The following are methods in which this is accomplished.

Synthesis Reactions: Synthesis reactions occur when two or more atoms bond together to form a more complex structure. Examples of this are the formation of glucagon from glucose molecules and the formation of tissue from amino acids.

Decomposition Reactions: Decomposition reactions are when more complex structures are broken down into simpler ones. An example of this is the decomposition of water molecules into H2 (hydrogen molecule) and O2 (oxygen molecule).

Exchange Reactions: Reactions in which two different kinds of molecules decompose into simpler structures, and then exchange those structures, to synthesize two completely different molecules. An example of this is the exchange reaction between lactic acid and sodium bicarbonate in the blood, in which these two break down, exchange molecules, and form sodium lactate and carbonic acid.

The Endocrine System

What is does?

The endocrine system maintains homeostasis within the body by controlling the body's cells. The responsibilities of the endocrine system are similar to that of the nervous system, however, the nervous system responds rapidly with nerve impulses, while the endocrine system responds overtime using the release and inhibition of hormones.

How hormones work:

Hormones are chemicals secreted from a cell into the body's extracellular fluid. Their purpose is to regulate the metabolic activity of the body's other cells. Hormones alter cellular activity, usually causing one of the following changes: changes in plasma membrane permeability or electrical state, synthesis of proteins or certain regulatory molecules in the cell, activation or inactivation of enzymes, or stimulation of mitosis.
There are two main groups of hormones: amino acid-based molecules and steroids. Both of these use different mechanisms to work on the body's target cells or organs. The following are the two mechanisms used.

  1. Steroid hormones (which are lipid soluble) diffuse through the plasma membrane of target cell.
  2. They then enter the nucleus.
  3. From their, they bind to a specific receptor protein
  4. That forms a hormone-receptor complex, which binds to specific sites on the cell's DNA
  5. This activates certain genes to transcribe messenger RNA (mRNA)
  6. Finally, the mRNA is translated in the cytoplasm, resulting in the synthesis of new proteins

Non-steroidal Hormones and the Second Messenger System
  1. Because protein and peptide hormones are not lipid soluble, they cannot enter the cell. Therefore, they bind to membrane receptors
  2. These in turn, set off a series of reactions that activate an enzyme.
  3. The enzyme catalyzes a reaction that produces a second-messenger molecule
  4. The second messenger molecule creates intracellular changes that create the typical target cell response to that specific hormone.


Hormone Control

Negative Feedback mechanisms are the main control of hormone release and retention in the body. Negative feedback decreases blood hormone levels because the already high blood hormone levels inhibit the release of more of that specific hormone.
The stimulus of the endocrine organs on the other hand falls into three different categories: Hormonal, Humoral, and Neural.
Hormonal Stimuli : when endocrine organs are stimulated by other hormones
Humoral Stimuli : when hormone release is affected by changing blood levels of certain ions and nutrients.
Neural Stimuli : when nerve fibers stimulate hormone release.

Organs of the Endocrine System


Pituitary Gland:

There are two parts to the pituitary gland, the anterior pituitary and the posterior pituitary. The anterior pituitary gland is often referred to as the master gland, because it controls the activities of many of the other endocrine organs. However, it is largely controlled by the hypothalamus and it's releasing and inhibiting hormones.The posterior pituitary gland on the other hand, is not completely an endocrine gland, as it does not produce the hormones that it releases. Rather, it stores some of the hormones produced by the hypothalamic neurons.

Hormones of the Anterior Pituitary:

  • Growth Hormone (GH): a metabolic hormone that directs the growth of skeletal muscles and long bones, as well as contributing to the building of amino acids into protein and stimulating cell growth.
    • Associated Disorders: Hyposecretion causes pituitary dwarfism. Hypersecretion causes gigantism. If hypersecretion occurs after growth has ended, it causes acromelagy.
  • Prolactin (PRL): a protein hormone that stimulates the growth of breast tissue and the continued production of milk.
  • Adrenocorticotropic Hormone (ACTH): regulates adrenal cortex
  • Thyroid-Stimulating Hormone (TSH): influences the growth of the thyroid gland.
  • Gonadotropic Hormones: various hormones that regulate the activities and growth of the gonads.
    • Follicle-Stimulating Hormone (FSH): stimulates follicle growth in the ovaries, allowing them to produce estrogen and eggs. In males, it stimulates sperm development by the testes.
    • Luteinizing Hormone (LH): triggers ovulation and the production of estrogen and progesterone in women.
      • In men, LH is Interstitial Cell-Stimulating Hormone (ICSH), which stimulates testosterone production

Hormones of the Posterior Pituitary:

  • Oxytocin: stimulates contractions of the uterine muscle in women during labor and sexual relations. It also causes milk ejection in nursing mothers.
  • Antidiuretic Hormone (ADH): inhibits urine production by causing the kidneys to reabsorb more water. ADH also increases blood pressure by constricting arterioles.

Thyroid Gland


Hormones of the Thyroid Gland

  • Thyroid Hormone: thyroid hormone is considered the major metabolic hormone and is made up of two hormones, thyroxine (T4) and triiodothyronine (T3). Together, they form thyroid hormone, which controls the rate at which glucose is burned, or oxidized, and converted to body heat and chemical energy.
  • Calcitonin (Thyrocalcitonin): decreases blood calcium levels by depositing calcium into the bones.
    • It is believed that calcitonin production dwindles down or stops in the elderly.

Parathyroid Gland


Hormones of the Parathyroid Gland

  • Parathyroid Hormone (PTH): increases blood calcium levels by destroying osteoclasts, which releases stored calcium into the blood.
    • often considered the most important regulator of calcium ion levels in the blood

Adrenal Glands


The adrenal glands are broken down into two parts, the adrenal cortex and the adrenal medulla. The medulla is within the adrenal cortex.

Hormones of the Adrenal Cortex

The hormones of the adrenal cortex are broken down into three groups: the mineralocorticoids, the glucocorticoids, and the sex hormones.
  • Mineralocorticoids
    • Aldosterone: controls blood sodium levels by reabsorbing or flushing out minerals via the kidneys
  • Glucocorticoids
    • Cortisone/Cortisol: maintain normal cell metabolism and protect the body against long-term stressors. They increase blood glucose levels, control inflammation and reduce pain.
  • Sex Hormones
    • Androgens and Estrogens are both produced in relatively small amounts within the adrenal cortex, although the majority of both of these are produced in the gonads.

Hormones of the Adrenal Medulla

  • Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline): enhance or prolong the effects of neurotransmitters during periods of intense stress (a fight/flight response). During this reaction, they also increase heart rate, blood pressure and blood circulation.

Pancreatic Islets (Islets of Langerhans)


The pancreatic islets are masses of hormone producing tissue within the tissue of the pancreas.

Hormones of the Pancreatic Islets

  • Insulin: lowers blood glucose levels
  • Glucagon: increases blood glucose levels

Pineal Gland


Hormones of the Pineal Gland

  • Melatonin: this hormone is a sleep trigger and it's level rise and fall during the day, changing the levels of tiredness and peaking at night.

Thymus Gland


Hormones of the Thymus Gland

  • thymosin: allows for the incubation of white blood cells during childhood


The male and female gonads produce different hormones.

Hormones of the Testes

  • Testosterone: stimulates the growth/development of male sex characteristics, stimulates the male sex drive, and stimulates the production of sperm. Testosterone also aids in the continued production of sperm throughout a males lifetime.

Hormones of the Ovaries

  • Estrogen: stimulates the development of secondary sex characteristics in woman as well as maintaining pregnancy and milk production.
  • Progesterone: quiets uterine muscles during pregnancy to protect the fetus,
    • Together, estrogen and progesterone prepare the uterus for a fertilized egg, creating the menstrual cycle.


The placenta is not considered an endocrine organ, however, it temporarily produces hormones in the fetus of pregnant women.
It produces human chorionic gonadotropin (hCG). This hormone stimulates the corpus luteum to continue to produce estrogen and progesterone, to prevent menses.

The Skeletal System

The Skeletal System is the system of bones in the human body. The skeleton is divided into two divisions, the axial skeleton and the appendicular skeleton, and along with the joints, cartilages, and ligaments, makes up the skeletal system.


Axial Skeleton: the axial skeleton is made up of the bones that form the longitudinal axis of the body (skull, vertebral column, thorax, sternum)

Appendicular Skeleton: the appendicular skeleton is made up of the limbs and girdles (femur, humerus, scapula, tibia, etc...)

Functions of the Bones

  1. Support: Form a frame that supports the bodies weight and the soft organs.
  2. Protection: The bones protect the bodies soft tissue organs
  3. Movement: Bones are used by the skeletal muscles as levers to allow for body movement.
  4. Storage: Fat is stored in the internal cavities of the bones. They also store minerals, such as calcium.
  5. Blood Cell Formation: Hematopoiesis, or blood cell formation, occurs in bone marrow.

The Different Kinds of Bones

Compact Bones

Compact bones are dense. They appear to be smooth and homogenous. Generally, compact bone is the outside layer of a bone.

Spongy Bone

Bone that is composed of small needle like pieces of bone and a lot of small cavities. This kind of bone can be found in the head of long bones.

Long Bones

Long bones are bones that are longer than they are wide, have a shaft with heads at both end and are, for the most part, compact bones. Examples of long bones are the femur, humerus, and the fibula, although there are many more.
The Structure of a Long Bone
Diaphysis: the shaft of the bone, made up of compact bone
Epiphyses: the ends of the bone, made up mostly of spongy bone

Short Bones

Short bones are usually cube shaped and are mostly made up of spongy bone. Examples of these are the bones of the wrist and ankle.

Flat Bones

These bones are thin, flattened and in general, are curved. Flat bones are comprised of two layers of compact bone, with a layer of spongy bone in the middle. The skull, ribs, and sternum are all examples of flat bones.

Irregular Bones

Irregular bones are just that, irregular. They do not fit any of the proceeding categories. These include the vertebrae and the hip bones.

Bone Marrow

There are two different kinds of bone marrow found in the bone.
Yellow Marrow (medullary): adipose tissue that is stored in the bone
Red Marrow: areas where red blood cells are formed.

Bone Formation, Growth and Remodeling

  • the skeleton of an embryo is made up of hyaline cartilage
    • bones develop using the hyaline cartilage structures as their models
      • This process is called ossification
        • first, the hyaline cartilage is covered with a bone matrix made up of osteoblasts
        • Then, the hyaline cartilage within the bone is digested, creating the medullary cavity of the new bone
  • At birth, most of the cartilage has become bone, except for articular cartilages, the cartilage that covers bone ends, and the epiphyseal plates
    • articular cartilages remain between joints for life
    • Epiphyseal plates allow for longitudinal growth.
      • The bone widens by adding osteoblasts to the peristoneum
        • Appositional Growth is this process of bone growth because they grow at the same time
          • Long bone growth is mainly controlled by growth hormone
          • Growth during puberty is mainly controlled by sex hormones
After growth stops, bones continue to change because of two factors
  1. Blood Calcium levels
  2. The pull of gravity and muscles on the skeleton
These remodeling factors allow the bones to remain proportional throughout a person's lifetime.

Types of Fractures

  • Comminuted Fractures: when the bone breaks in many fragments
    • Common with the elderly
  • Compression Fractures: When the bone is crushed
    • Common in porous bones
  • Depressed Fractures: when the broken bone portion is pushed in
    • Common in skull fractures
  • Impacted Fractures: when the broken bone ends are pushed together
    • common in fall injuries
  • Spiral Fractures: When a ragged break occurs due to an excessive twisting force
    • Common in sports fractures
  • Greenstick Fractures: When a bone breaks incompletely
    • Common in children who's bones are still flexible

How Bones are Repaired

  1. A hematoma is formed. A hematoma is a blood-filled swelling, which results from the ruptured blood-vessels. This prevents the bone cells from dying.
  2. The break is splinted by a fibrocartilage callus. This includes the growth of new capillaries and the disposal of dead tissue. Only after this occurs does the fibrocartilage callus form, which is a mass of repair tissue, made up of some cartilage matrix, bony matrix, and collagen fibers. This splints the broken bone and closes the gap.
  3. The bony callus is formed. The bony callus, which is made up of spongy bone, occurs as more osteoblasts and osteoclasts arrive into the area where the bone was broken. This gradually changes the fibrocartilage callus into the bony callus.
  4. Finally, bone remodelling occurs. The bony callus is remodeled to form a strong permanent patch at the fracture site.

The Axial Skeleton



The skull is made up of the cranium, which is made up of eight flat bones that encase the brain, and the facial bones, which is made up of fourteen bones and also holds the eyes and the facial muscles.


  • Frontal Bone
    • Forms the forehead, the bony projections under the eyebrows, and the superior part of the eye orbitals.
  • Parietal Bones
    • Paired bones
    • Form most of the superior and lateral walls of the cranium.
    • Meet at the midline of the skull and are connected by the sagittal suture
    • Form the coronal suture with the frontal bone
  • Temporal Bones
    • Paired bones, inferior to the parietal bones
    • Connect to the parietal bones by the squamous sutures
    • Bone Markings of the Temporal Bones:
  • Occipital Bone
    • The most posterior bone of the skull, which forms the floor and back wall of the skull.
    • Connects to the parietal bones with the lambdoid suture.
    • At the base of the occipital bone is the foramen magnum, which allows the spinal cord to connect to the brain.
  • Sphenoid Bone
    • Forms part of the floor of the cracium.
    • Contains the sella turcica, which holds the pituitary gland
    • Contains many air cavities known as the sphenoid sinuses
  • Ethmoid Bone
    • Anterior to the sphenoid.
    • Forms the roof of the nasal cavity and the medial walls of teh orbit.

Facial Bones

  • Maxillae
    • Form the upper jaw
    • Joins with all facial bones except the mandible
    • Contains the palatine processes, which form the anterior part of the hard palate of the mouth
    • Contains the paranasal sinuses
  • Palatine Bones
    • Posterior to the palatine processes of the maxillae
    • Forms the posterior part of the hard palate.
  • Zygomatic Bones
    • They are the cheekbones.
    • Form part of the lateral walls of the orbits.
  • Lacrimal Bones
    • Form the medial walls of the orbit

  • Nasal Bones
    • Form the bridge of the nose
  • Vomer Bone
    • Forms most of the nasal septum
  • Inferior Nasal Concha
    • Project from the walls of the naval cavity
  • Mandible
    • This is the lower jaw.
      • Strongest and largest bone of the face
    • The mandible is the only freely movable joint in the skull.

The Fetal Skull

The fetal skull is very different from an adult skull. First of all, the infant's skull is very large compared to the infant's total body length (it is about one fourth of the body's length, compared to an adult's, which is one eighth). Also, the skull is still mainly made up of hyaline cartilage, which will later be ossified to become the adult skull. Finally, fetal skulls also have fontanels, fibrous membranes that connect the cranial bones. These allow the infants brain to be slightly compressed during the birthing process.


The Vertebral Column

The vertebral column, or spine, extends from the skull to the pelvis. It supports the weight of the upper body and disperses the weight between the lower limbs. The adult spine is made up of 26 irregular bones, which contain the spinal cord. Between the vertebrae are intervertebral discs, which cushion the vertebrae, absorb shock, and allow flexibility. The spine is separated into three different sections:
  • Cervical Vertebrae: the first seven vertebrae make up the cervical spine. Of these, the first is called the atlas and the second the axis. The allow a persons skull to move up and down and side to side, respectively. The cervical spine as a whole is concave.
  • Thoracic Vertebrae: the next twelve vertebrae make up the thoracic spine. This part of the spine is convex.
  • Lumbar Vertebrae: the final five vertebrae make up the lumbar spine. This area is concave and made up of the largest and sturdiest vertebrae. These support the most stress of the vertebral column.
At birth, humans are born with 33 vertebrae, however, as the body matures, these fuse together to form the sacrum and the coccyx. The sacrum is the posterior wall of the pelvis, and it fuses with the hip bones via the sacroiliac joints. The coccyx is the human tailbone, and is a remnant of the tail that other vertebrate animals have.

The Bony Thorax

The bony thorax is made up of the sternum, ribs, and thoracic vertebrae. The function of the bony thorax is to protect the organs in the thoracic cavity.


The sternum is often referred to as the breast bone. It is made up of the fusion of three bones, the manubrium, the body, and the xiphoid process.
The sternum is attached to the first seven pairs of ribs, known as the true ribs, creating the cage surrounding the organs.

The Appendicular Skeleton

The Shoulder Girdle

The role of the shoulder girdle is to attach the upper limbs, arms, to the axial skeleton. Each shoulder girdle is made up of two bones, a clavicle and a scapula. The clavicle acts to hold the arms away from the thorax, while preventing the shoulder from dislocating. The scapula on the other hand, allows the arm to slide back and forth against the thorax.

The Arm

The arm is formed by the humerus. The head of the humerus, at the proximal end of the bone, fits into the glenoid cavity of the scapula, holding it in place within the shoulder girdle. At the distal end, the humerus has two projections, the greater and lesser tubercles, which are muscle attachments. On the distal end of the bone, there is also the medial trochlea and the capitulum, which articulate with the radius and ulna of the forearm.

The Forearm

There are two bones that make up the lower arm, the radius and the ulna. When the body is in anatomical position, the radius is the lateral bone. The radius and the ulna are connected via the radioulnar joints, with interosseous membrane connecting the length of the bones. The proximal end of the radius forms a joint with the capitulum of the humerus. The ulna articulates with the humerus at the trochlea, where the ulna's coronoid process and olecranon process attach to the trochlea.

The Hand

The hand is made up of three bone groups: the carpals, the metacarpals and the phalanges. There are eight carpal bones which form the wrist. Then, the palm of the hand is made up of the metacarpals. There are five of these, which articulate with the phalanges. There are fourteen phalanges on each hand that make up the fingers. Each finger is made up of three phalanges, except for the thumb, which only has two.

The Pelvic Girdle

The pelvic girdle is made up of the coxal, or hip, bones. Each of these hip bones is made up of the fusion of three bones, the ilium, ischium and pubis. These three bones create a socket called the acetabulum, which the head of the hip bone goes into.
There are several differences between the male and female pelvis. The female pelvis has a larger, more circular inlet, is shaller, the ilia are more flared, it has a shorter sacrum, and the pubic arch is more rounded and has a greater angle.


The femur makes up the thigh, it is the strongest and heaviest bone in the body. The proximal end has a head, which is joined to the pelvis in a ball and socket joint with the acetabulum. Because the femur slants medially, the knees can be at the body's center of gravity. At the distal end of the femur, there are the lateral and medial condyles, which articulate with the lower leg. On the anterior surface of the distal femur there is the patellar surface, which joins with the patella to form the kneecap.

Lower Leg

The lower leg is made up of the tibia and the fibula. The tibia is the medial bone, and joins with the femur to create the knee. The tibia and fibula are connected by the tibiofibular joint, with interosseous membrane extending their lengths. At the distal ends of the tibia and the fibula are the medial malleolus and the lateral malleolus, which create the ankle bone respectively.


Like the hand, the foot is made up of three separate kinds of bones. The tarsals, metatarsals and phalanges make up the length of the foot. There are seven tarsals in the foot. The largest is the calcaneus, and the second is the talus. These are the bones between the lateral and medial malleolus that make up the ankle. The metatarsals make up the sole of the foot and there are five of them. Finally, there are fourteen phalanges, which form the toes. Once again like the hand, each toe has three phalanges while the big toe has two.
The foot is made up of three different arches. Two of these, the medial and lateral, are longitudinal, while one is transverse.


Joints allow our bodies to move, because without them, there would be no capability to move the bones. There are two ways to classify the bones.
Functional Classifications:
  • Synarthroses joints: immovable joints
  • Amphiarthroses joints: slightly movable joints
  • Diarthroses Joitns: Freely moving joints
Structural Classifications:
  • Fibrous Joints
    • connected by fibrous tissues and are synarthroses.
      • Examples: skulles sutures
  • Cartiloginous Joints
    • bone ends that are connected by cartilage. In general, these are amphiarthroses, although sometimes they cannot move at all.
      • Examples: pubic symphysis
  • Synovial Joints
    • these are articulated bone ends that are separated by a joint cavity, filled with synovial fluid
    • All of these have articular cartilage (forms the joint), fibrous articular capsule (encloses joint), a joint cavity (contains synovial fluid), and reinforcing ligaments (enforces the fibrous capsule).
      • Examples: Joints of the limbs
Types of Synovial Joints
  • Plane Joint: flat articular surfaces, allows for slipping or gliding movements.
  • Hinge Joint: a cylinder shaped bone end fits into a trough shaped surface in another bone. Allows angular movement.
  • Pivot Joint: rounded bone end fits into a sleeve or ring of bones or ligaments. Allow for rotation.
  • Saddle Joint: a convex and concave area that fits together.
  • Ball and Socket Joint: spherical bone head fits into a rounded socket. Allows movement in all axes.

The Muscular System

Muscles allow the body to move. Their main function in the body is to contract, or shorten, which moves the bones, creating movement. The more specific purposes of muscles are to produce movement, maintain posture, stabilize joints, and generate heat.

Muscle Types

  1. Skeletal Muscles: These are striated and voluntary muscles that act as anchors, provide durability, movement, and conserve space.
    1. These are made up of skeletal muscle fibers, which are shaped like elongated ovals, and are multinucleate cells.
  2. Smooth Muscles: Muscles that make up the walls of visceral organs, like the stomach, bladder, and respiratory passages. It makes involuntary movements and is not striated.
    1. These are made up of smooth muscle cells, which are spindle-shaped. They also have a single-nucleus.
      1. Usually, smooth muscle cells are found in two layers, one which runs circularly, and another that runs longitudinally.
  3. Cardiac Muscle: This kind of muscle is found solely in the heart. It moves involuntarily and is striated
    1. Cadiac muscles are organized into bundles, each of which is surrounded by soft connective tissue.

Microscopic Anatomy of Skeletal Muscle

The parts of a Skeletal Muscle Cell
  • Sarcolemma: several oval nuclei that are found under the plasma membrane
  • Myofibrils: Ribbonlike organelles that surround the sarcolemma. Made up of sarcomeres
    • Myofibrils are made up of alternating light (I) and dark (A) bands
  • Sarcomeres: chains of contractile units.
  • Myofilaments: threadlike proteins, within sarcomeres
    • Made up of thick filaments, or myosin filaments, which are make up of bundles of myosin, and thin filaments, which are made up of actin.
  • Sarcoplasmic Reticulum: specialized smooth ER, which surround myofibrils.

Skeletal Muscle Activity

Functions that enable muscles to perform their duties are irritability, or the ability to receive stimuli, and contractility, which is the ability to shorten when adequate stimulus is received.

Nerve Stimulus and Action Potential

Motor neurons stimulate muscle cells, together, creating a motor unit. There are also axons, or nerve fibers, that reach out, branching into several axon terminals, and form junctions with the sarcolemma of several muscle cells. This forms a neuromuscular junction.
When a nerve impulse travels through the axon terminals, it releases a neurotransmitter, in this case, acetylcholine (ACh), which attaches to the membrane proteins of the sarcolemma. ACh makes the local sarcolemma more temporarily more permeable to sodium ion, which rush into the muscle cell, as potassium rushes out. This transaction makes the cell's interior positive. This causes action potential to occur, allowing the rest of the muscle cell to contract.
  • The products of this reaction include:
    • Acetic Acid
    • Choline
A single nerve impulse creates only one contraction.


Sliding Filament Theory

Myosin heads, which protrude from the thick filaments of the myofilaments, attach to the thin actin filaments, via binding sites. This occurs when calcium ions enter the muscle cell from the sarcoplasmic reticulum, causing the attachment of the myosin cross bridges to the actin. Once this has occurred, ATP allows the cross bridges to detach and reattach to different actin sites, generating tension and allowing the filament to slide. This allows the muscle to contract.
Once the reaction has occurred, the calcium returns to the sarcoplasmic reticulum.

Muscle Contraction as a Whole

One muscle cell never partially contracts, it always contracts wholly. However, since skeletal muscles consist of thousands of cells, there are graded responses, or varying degrees of shortening, that are the results of varying stimuli.
Graded Responses can be produced by:
  • by changing the frequency of muscle stimulation
  • by changing the number of muscle cells being stimulated

Energy for Muscle Contraction

Muscles store approximately 4 to 6 seconds worth of energy, which comes from hydrolyzed ATP. However, ATP is the only energy source that can be generated directly to power the muscle, and it must be almost constantly regenerated.
Three Pathways of ATP Regeneration:
  • Direct Phosphorylation of ADP by creatine phosphate: a high energy phosphate group is transferred from Creatine Phosphate, given to ADP to create ATP. (Exhausted is about 20 seconds).
  • Aerobic Respiration: The break down of glucose to carbon dioxide and water, with the energy released being captured by the bonds of ATP molecules. This is fairly slow, and delivers constant energy.
  • Anaerobic glycolysis and lactic acid formation: Glucose is broken down into pyruvic acid, and small amounts of energy is captured in ATP bonds.

Muscle Fatigue and Oxygen Debt

  • Muscle fatigue occurs when the muscle is unable to contract even though is it still being stimulated.
    • Often, this results from oxygen debt, meaning that the person is not taking in as much oxygen as they are using, causing lactic acid to build up. Also, a lack of ATP occurs, the combination of both causing the muscle to contract less effectively.

Muscle Contractions

  • Isotonic Contractions: occurs when muscle filaments are successful in their sliding movements
  • Isometric Contractions: occurs when a muscle tries to slide but is unable to because they are pulling against something immovable.

Types of Body Movements

  • Flexion: decreases the angle of the joint, and brings two bones closer together. Example: bending the knee towards the hamstrings.
  • Extension: Opposite of flexion. When the angle of the joint is increased. Example: Straightening the knee
    • Hyperextension is increasing the angle more than 180 degrees.
  • Rotation: Movement of the bone around its longitudinal axis. Example: Shaking your head no.
  • Abduction: Moving a limb away from the midline. Example: Lifting your leg to the side.
  • Adduction: Moving a limb towards the midline. Example: Bringing your leg to a standing position after abducting it.
  • Circumduction: Combination of flexion, extension, abduction, and adduction. Generally, when the proximal end is stationary and the distal end is moving in a circle.
  • Special Movements:
    • Dorsiflexion
    • Plantar Flexion
    • Supination
    • Pronation
    • Opposition
    • Inversion
    • Eversion

Roles of the Skeletal Muscles

Prime Movers are the muscles that are mainly responsible for causing a particular movement.
Synergists help prime movers produce movement or reduce resistance
Antagonists are muscles that work against the actions of the prime movers
Fixators are muscles that hold a bone still or stabilize the origin.

Naming Muscles

  • Direction of the Muscle Fibers
  • Relative size of the Muscles
  • Location of the Muscle
  • Number of Origins
  • Location of the Muscle's Origin and Insertion
  • Shape of the Muscle
  • Action of the Muscle

Arrangement of Fascicles

  • Circular: when fascicles are arranged in concentric rings
    • generally around body openings
  • Convergent: converge towards a single insertion point.
  • Parallel: when fascicles run parallel
  • Fusiform: spindle shaped muscle with an expanded belly
  • Pennate: short fascicles that extend obliquely to a central tendon.

Skeletal Muscles

Facial Muscles

  • Frontalis: raises eyebrows and wrinkles the forehead. Runs over the frontal bone.
  • Orbicularis Oculi: closes, blinks, squints and winks eyes.
  • Orbicularis Oris: Circular muscle around the lips that closes the mouth and protrudes the lips.
  • Buccinator: Horizontally across the cheek. Flattens the cheeks and helps to chew because it compresses the cheek.
  • Zygomaticus: Smiling muscle because it raises the corners of the mouth.

Chewing Muscles

  • Masseter: covers the lower jaw. Elevates the mandible.
  • Temporalis: Covers the temporal bone. Synergist in closing the jaw.

Neck Muscles

  • Platysma: Covers the anterolateral neck. Pulls corners of the mouth inferiorly, producing a downward sag.
  • Sternocleidomastoid: One on each side of the neck. When they contract together, the sternocleidomastoids flex the neck. When just one contracts, it rotates the head to the opposite side.

Trunk Muscles

  • Pectoralis Major: Covers the upper part of the chest. Adducts and flexes the arm.
  • Intercostal Muscles: Muscles found between the ribs. Help in breathing by raising the rib cage to breath in. Then depress the rib cage to move the air out of the lungs.
  • Rectus Abdominis: run from the pubis to the rib cage. Allow the flexion of the vertebral column.
  • External Oblique: Make up the lateral walls of the abdomen. Flex the vertebral column, rotate the trunk, and bend it laterally.
  • Internal Oblique: Originate from the iliac crest and insert into the last three ribs. Have the same functions as the external oblique.
  • Transversus Abdominis: Runs horizontally across the abdomen. Compresses the abdominal contents.
  • Trapezius: Run from the neck and upper trunk. These muscles can elevate, depress, adduct and stabilize the scapula.
  • Latissimus Dorsi: Originates from the lower spine and inserts into the proximal humerus. It extends and adducts the humerus.
  • Erector Spinae: Prime mover of back extension. Spans the vertebral column and is made up of three muscles ( longissimus, iliocostalis, and spinalis). Helps control the action of bending over.
  • Deltoid: Goes across the shoulder girdle from the spine of the scapula to the clavicle and is the prime mover of arm abduction.

Muscles of the Upper Limb

  • Biceps Brachii: Originates at the shoulder girdle and inserts at the radial tuberosity. Prime Mover in the flexion of the forearm and acts to supinate the forearm.
  • Brachialis: Located underneath the biceps brachii, it assists in elbow flexion.
  • Brachioradialis: Originates from the humerus and inserts into the distal forearm.
  • Triceps Brachii: Originates from the shoulder girdle and the proximal humerus and inserts into the olecranon process of the ulna. Prime mover of elbow extension. Antagonist of the biceps brachii.