1) Storage - the stomach allows a meal to be consumed and the materials released incrementally into the duodenum for digestion. It may take up to four hours for food from a complete meal to clear the stomach. 
2) Chemical digestion - pepsin begins the process of protein digestion cleaving large polypeptides into shorter chains . 
3) Mechanical digestion - the churning action of the muscularis causes liquefaction and mixing of the contents to produce acid chyme. 
4) Some absorption - water, electrolytes, monosaccharides, and fat soluble molecules including alcohol are all absorbed in the stomach to some degree.

The thyroid gland is a double-lobed structure located in the neck. Embedded in its rear surface are the four parathyroid glands.

The Thyroid Gland

The thyroid gland synthesizes and secretes:

• thyroxine (T₄) and
• calcitonin

T₄ and T₃

Thyroxine (T₄ ) is a derivative of the amino acid tyrosine with four atoms of iodine. In the liver, one atom of iodine is removed from T₄ converting it into triiodothyronine (T₃). T₃ is the active hormone. It has many effects on the body. Among the most prominent of these are:

• an increase in metabolic rate
• an increase in the rate and strength of the heart beat.

The thyroid cells responsible for the synthesis of T₄ take up circulating iodine from the blood. This action, as well as the synthesis of the hormones, is stimulated by the binding of TSH to transmembrane receptors at the cell surface.

Diseases of the thyroid

1. hypothyroid diseases; caused by inadequate production of T₃

• cretinism: hypothyroidism in infancy and childhood leads to stunted growth and intelligence. Can be corrected by giving thyroxine if started early enough.
• myxedema: hypothyroidism in adults leads to lowered metabolic rate and vigor. Corrected by giving thyroxine.
• goiter: enlargement of the thyroid gland. Can be caused by:
  • inadequate iodine in the diet with resulting low levels of T₄ and T₃;
  • an autoimmune attack against components of the thyroid gland (called Hashimoto's thyroiditis).

2. hyperthyroid diseases; caused by excessive secretion of thyroid hormones

Graves´ disease. Autoantibodies against the TSH receptor bind to the receptor mimicking the effect of TSH binding. Result: excessive production of thyroid hormones. Graves´ disease is an example of an autoimmune disease.

Osteoporosis. High levels of thyroid hormones suppress the production of TSH through the negative-feedback mechanism mentioned above. The resulting low level of TSH causes an increase in the numbers of bone-reabsorbing osteoclasts resulting in osteoporosis.

Calcitonin

Calcitonin is a polypeptide of 32 amino acids. The thyroid cells in which it is synthesized have receptors that bind calcium ions (Ca²⁺) circulating in the blood. These cells monitor the level of circulating Ca²⁺. A rise in its level stimulates the cells to release calcitonin.

• bone cells respond by removing Ca²⁺ from the blood and storing it in the bone
• kidney cells respond by increasing the excretion of Ca²⁺

Both types of cells have surface receptors for calcitonin.

Because it promotes the transfer of Ca²⁺ to bones, calcitonin has been examined as a possible treatment for osteoporosis

The Adrenal Glands

The adrenal glands are two small structures situated one at top each kidney. Both in anatomy and in function, they consist of two distinct regions:

• an outer layer, the adrenal cortex, which surrounds
• the adrenal medulla.

The Adrenal Cortex

cells of the adrenal cortex secrete a variety of steroid hormones.

• glucocorticoids (e.g., cortisol)
• mineralocorticoids (e.g., aldosterone)
• androgens (e.g., testosterone)

• Production of all three classes is triggered by the secretion of ACTH from the anterior lobe of the pituitary.

Glucocorticoids

They Effect by raising the level of blood sugar (glucose). One way they do this is by stimulating gluconeogenesis in the liver: the conversion of fat and protein into intermediate metabolites that are ultimately converted into glucose.

The most abundant glucocorticoid is cortisol (also called hydrocortisone).

Cortisol and the other glucocorticoids also have a potent anti-inflammatory effect on the body. They depress the immune response, especially cell-mediated immune responses. 

Mineralocorticoids

The most important of them is the steroid aldosterone. Aldosterone acts on the kidney promoting the reabsorption of sodium ions (Na⁺) into the blood. Water follows the salt and this helps maintain normal blood pressure.

Aldosterone also

• acts on sweat glands to reduce the loss of sodium in perspiration;
• acts on taste cells to increase the sensitivity of the taste buds to sources of sodium.

The secretion of aldosterone is stimulated by:

• a drop in the level of sodium ions in the blood;
• a rise in the level of potassium ions in the blood;
• angiotensin II
• ACTH (as is that of cortisol)

Androgens

The adrenal cortex secretes precursors to androgens such as testosterone.

Excessive production of adrenal androgens can cause premature puberty in young boys.

In females, the adrenal cortex is a major source of androgens. Their hypersecretion may produce a masculine pattern of body hair and cessation of menstruation.

Addison's Disease: Hyposecretion of the adrenal cortices

Addison's disease has many causes, such as

• destruction of the adrenal glands by infection;
• their destruction by an autoimmune attack;
• an inherited mutation in the ACTH receptor on adrenal cells.

Cushing's Syndrome: Excessive levels of glucocorticoids

In Cushing's syndrome, the level of adrenal hormones, especially of the glucocorticoids, is too high.It can be caused by:

• excessive production of ACTH by the anterior lobe of the pituitary;
• excessive production of adrenal hormones themselves (e.g., because of a tumor), or (quite commonly)
• as a result of glucocorticoid therapy for some other disorder such as
  • rheumatoid arthritis or
  • preventing the rejection of an organ transplant.

The Adrenal Medulla

The adrenal medulla consists of masses of neurons that are part of the sympathetic branch of the autonomic nervous system. Instead of releasing their neurotransmitters at a synapse, these neurons release them into the blood. Thus, although part of the nervous system, the adrenal medulla functions as an endocrine gland.The adrenal medulla releases:

• adrenaline (also called epinephrine) and
• noradrenaline (also called norepinephrine)

Both are derived from the amino acid tyrosine.

Release of adrenaline and noradrenaline is triggered by nervous stimulation in response to physical or mental stress. The hormones bind to adrenergic receptors  transmembrane proteins in the plasma membrane of many cell types.

Some of the effects are:

• increase in the rate and strength of the heartbeat resulting in increased blood pressure;
• blood shunted from the skin and viscera to the skeletal muscles, coronary arteries, liver, and brain;
• rise in blood sugar;
• increased metabolic rate;
• bronchi dilate;
• pupils dilate;
• hair stands on end (gooseflesh in humans);
• clotting time of the blood is reduced;
• increased ACTH secretion from the anterior lobe of the pituitary.

All of these effects prepare the body to take immediate and vigorous action.

The cell membrane is called the sarcolemma. This membrane is structured to receive and conduct stimuli. The sarcoplasm of the cell is filled with contractile myofibrils and this results in the nuclei and other organelles being relegated to the edge of the cell.

Myofibrils are contractile units within the cell which consist of a regular array of protein myofilaments. Each myofilament runs longitudinally with respect to the muscle fiber. There are two types: the thick bands and the thin bands. Thick bands are made of multiple molecules of a protein called myosin. The thin bands are made of multiple molecules of a protein called actin. The thin actin bands are attached to a Z-line or Z-disk of an elastic protein called titin. The titin protein also extends into the myofibril anchoring the other bands in position. From each Z-line to the next is a unit called the 

    The sarcomere is the smallest contractile unit in the myofibril. Sarcomeres contract because the Z-lines move closer together. As the sarcomeres contract the myofibrils contract. As the myofibrils contract the muscle cell contracts. And as the cells contract the entire muscle contracts.

The arrangement of the thick myosin filaments across the myofibrils and the cell causes them to refract light and produce a dark band known as the A Band. In between the A bands is a light area where there are no thick myofilaments, only thin actin filaments. These are called the I Bands. The dark bands are the striations seen with the light microscope.

1. Automatic control (sensory) of respiration is in - brainstem (midbrain) 

2. Behavioral/voluntary control is in - the cortex

3. Alveolar ventilation -the amount of atmospheric air that actually reaches the alveolar per breath and that can participate in the exchange of gasses between alveoli and blood

4. Only way to increase gas exchange in alveolar capillaries - perfusion-limited gas exchange 

5. Pulmonary ventiliation not effected by - concentration of bicarbonate ions

6. Central chemoreceptors - medulla -  CO2, O2 and H+ concentrations

7. Peripheral chemoreceptors - carotid and aortic bodies- PO2, PCO2 and pH 

8. Major stimulus for respiratory centers - arterial PCO2 

9. Rhythmic breathing depends on 
1. continuous (tonic) inspiratory drive from DRG (dorsal respiratory group)
2. intermittent (phasic) expiratory input from cerebrum, thalamus, cranial nerves and ascending spinal cord sensory tracts

10. Primary site for gas exchange - type I epithelial cells for alveoli

Functions of the nervous system:

1) Integration of body processes

2) Control of voluntary effectors (skeletal muscles), and mediation of voluntary reflexes.

3) Control of involuntary effectors (  smooth muscle, cardiac muscle, glands) and mediation of autonomic reflexes (heart rate, blood pressure, glandular secretion, etc.)

4) Response to stimuli

5) Responsible for conscious thought and perception, emotions, personality, the mind.