During inspiration, the diaphragm moves downward and contracts. The contracted diaphragm creates negative air pressure in the expanded lungs and air moves into the alveoli in the lungs. During expiration, the diaphragm moves upward and expands. It creates positive air pressure in the constricted lungs and air moves out of the alveoli.

Alveoli are air sacs that function as the location for gas exchange in the lungs. The pharynx, larynx, and bronchioles are the route for air passage. The epiglottis is a flap of tissue that prevents food from entering the respiratory tract.

In this question, CO₂ travels from capillaries out through the nasal cavity via the lungs. Capillaries → anterior or posterior vena cava → right atrium → right ventricle → pulmonary artery → pulmonary capillaries → alveoli → bronchioles → bronchi → trachea → larynx → pharynx → out through the nasal cavity. It’s a long journey!!

An artery is a large vessel with a thick muscular wall to resist the high pressure. The thinnest and smallest vessels are the capillaries, which function to exchange gas, nutrients, and waste with body cells. Venules connect capillaries and veins. Vessels that transport blood into the heart are called veins. Veins have low blood pressure, so there are valves to prevent back flow.

Cholecystokinin (CCK) and enterogastrone are hormones secreted by the duodenum. CCK stimulates the production of bile from the gall bladder and pancreatic enzymes. Enterogastrone inhibits gastric secretion and motility of the stomach. Gastrin stimulates the production of gastric juices in the stomach. Glucogon and insulin, hormones for the regulation of blood glucose levels, are secreted by the pancreas. Glucogon increases blood glucose, while insulin decreases blood glucose.

All are true for the adrenal cortex except B. The adrenal cortex responds to long term stress. The adrenal medulla, stimulated by the hypothalamus, secretes epinephrine and norepinephrine hormones for the short term stress response.

Insects have hemolymph fluid, in which blood and interstitial fluid are the same. Fish have two chambers and one circuit in a closed circulatory system. Frogs use lungs and skin to exchange O₂ and CO₂ and have three chambers and two circuits. Birds and mammals have the most well developed circulatory system, with four chambers and two circuits.

All are true. Gas exchange occurs between alveolar spaces and capillaries of the lungs. Partial pressure of O₂ in the alveolar spaces is higher than in the capillaries of the lungs, so that O₂ moves from the alveolar spaces into the capillaries of the lungs. Partial pressure of CO₂ in the capillaries of the lungs, however, is higher than the alveolar spaces, so CO₂ flows from the capillaries of the lungs to the alveolar spaces. Before these gases are exchanged, CO₂ and O₂ have to pass through the moist area by diffusion. Birds have different air passageways for inhalation and exhalation. One direction of air passes through tiny parallel tubes called parabronchi. The capillaries of the body have the largest area, so the velocity of blood flow is lower than in any other vessel.

Polysaccharides begin to be broken down into disaccharides (not monosaccharides) by salivary amylase in the mouth. In the stomach protein is digested only by pepsin and in the small intestine fat is broken down into glycerol and fatty acid by pancreatic lipase.

Steroid hormones (such as androgens, estrogens, progesterone, cortisol, and aldosterone) can bind to receptors in the nucleus through plasma membranes. Most other hormones, like antidiuretic hormones, are peptide hormones.

External respiration means O₂ and CO₂ exchange outside of the cells. Exchanging gas between lungs and pulmonary capillaries, transporting gas, and exchanging gas between systemic capillaries and cells are all external respiration.

In the villi of the small intestine, fatty acid and glycerol are absorbed by lacteals and moved to the blood via lymph vessels. Glucose and amino acids are absorbed by blood capillaries and moved to the liver via hepatic portal vessels. Parietal cells and chief cells are in the stomach.

Passage of waste product from renal system to out of body: Glomerulus → Bowman’s capsule → proximal tubule → descending loop of Henle → ascending loop of Henle → distal tubule → collecting duct → ureter → urinary Bladder → urethra. As waste product passes through each stage, the concentration of urea becomes higher.

Plasma proteins are albumin, fibrinogen, and immunoglobulins. Albumin regulates osmotic balance or blood pressure and pH buffering. Fibrinogen is one component for blood clotting, and immunoglobulins are antibodies. Thrombin is an enzyme, which converts fibrinogen to fibrin in blood clotting. Myoglobin is a protein with a monomer shape, which binds O₂ and is stored in muscles.

Vitamin A, also called retinal, is a fat soluble vitamin that is important for the functioning of photoreceptors of the retina. Dietary deficiency of Vitamin A can cause vision problems.

All are true. The pancreas secretes bicarbonate ions, amylase, lipase, and trypsin as an exocrine gland and also secretes glucagons and insulin hormones as an endocrine gland.

Aldosterone hormone, secreted by the adrenal cortex, reabsorbs water and sodium at distal tubules in the kidney and increases blood pressure. Thyroid stimulating hormone (TSH), secreted by the anterior pituitary, stimulates the thyroid to release T₃ and T₄ for controlling homeostatic functions and cellular metabolism. Antidiuretic hormone (ADH) stimulates the kidney to reabsorb water. Growth hormone (GH) stimulates liver and bone for increasing cell size and cell division. ACTH, secreted by the anterior pituitary, stimulates the adrenal cortex to produce aldosterone and cortisol hormones for the long term stress response.

Air passage from outside the body into the lungs:

Nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli

In high elevations the differences of partial O₂ and CO₂ pressures decreases because of low atmospheric pressure. Therefore, the gas exchange rates between alveolar spaces and alveolar capillaries decrease and the gas-exchange rates between tissue capillaries and tissue cells also decreases. Finally, the person can hardly breath and becomes tired. Circulation of blood is related to cardiac pressure.

A and C are correct. Red blood cells transport O₂ and CO₂. They lack nuclei and mitochondria, and cannot repair themselves. Basophils secrete chemical histamine to damaged tissue or allergic reaction. Lymphocyte has T cells and B cells. B cells make antibodies from plasma cells. Monocytes become macrophages.

Increased metabolism rates increase body temperatures and partial blood pressure of CO₂ and decrease blood pH level. Therefore, the O2 binding affinity of hemoglobin is decreased.

The medulla oblongata controls pH level by detecting CO₂ concentration in the blood. The breathing speed increases when the blood CO₂ level is high, while the breathing speed decreases when the blood CO₂ level is low.

Calcitonin, released by the thyroid gland, reduces the blood calcium levels by osteoblasts of bone. PTH (parathyroid hormone), released by the parathyroid gland, raises the blood calcium levels by osteoclasts of bone. TSH (thyroid stimulation hormone) stimulates the thyroid to control homeostatic functions and cellular metabolism. Glucagon increases blood glucose.

Minerals are inorganic nutrients that are regulated by the excretion of urine or sweat. Important minerals in the body are sodium, potassium, calcium, phosphorus, magnesium, chlorine, and sulfur.

Vitamins are not inorganic nutrients but organic compounds; so, vitamins are not minerals.

K⁺ is one important factor in neurons. Vitamin K, Ca²⁺, and platelets are clotting materials, which convert a prothrombin to an active thrombin enzyme. Fibrin converted by thrombin forms the framework of a clot at the site of damaged tissue.

All are true. The liver has multiple functions, such as bile production, destruction of red blood cells, glycogen synthesis and breakdown, synthesis of plasma proteins, conversion of ammonia into urea, and detoxification.

Passage of waste product from renal system to out of body: Glomerulus → Bowman’s capsule → proximal tubule → descending loop of Henle → ascending loop of Henle → distal tubule → collecting duct → ureter → urinary Bladder → urethra

The anterior pituitary secretes GH, TSH, ACTH, LH, FSH, prolactin, and MSH, while the posterior pituitary secretes ADH and oxytocin.

Animals use chemical substances to communicate with each other by odors outside the body. These substances are called pheromones. Pheromones function in courtship, marking territory, and classifying social order between members of the same species.

The amount of blood pumped from the ventricle is called stroke volume.

Eosinophils, monocytes, and neutrophils are phagocytic cells. Platelets function in the process of blood clotting.

Most clean and oxygenated blood is contained in the pulmonary vein because this blood is from the lungs right after oxygenation, while most deoxygenated blood is contained in the anterior and posterior vena cava. The capillaries have the lowest velocity of blood.

Bile containing bile salts and bicarbonate is made by the liver and stored in the gall bladder. Bile salts are not enzymes but used only for emulsification of fat in the small intestine.

The cardiac orifice regulates the passage of food between esophagus and stomach. If it does not work, the strong acid chyme in the stomach may back flow to the esophagus and burn the esophagus lining. The upper esophageal sphincter controls the food passage between pharynx and esophagus and the pyloric sphincter controls the passage of acid chyme between the stomach and small intestine. Peristalsis is a wave of muscular contraction in the esophagus. Chief cells secrete pepsin in the stomach.

Water, glucose, and small solutes are filtrated from glomerulus to Bowman’s capsule. Salt and water are secreted or reabsorbed between distal tubule and peritubular capillary.

Filtration means that protein-free plasma is filtered by active transport from the glomerulus to Bowman’s capsule. Reabsorption is the movement of salts, water, and nutrients from the renal tubule to peritubular capillaries. Especially water is reabsorbed by osmosis (passive transport) at the descending loop of Henle.

One of the metabolic disorders of the thyroid gland is hypothyroidism, which is caused by insufficient secretion of thyroid hormone. Symptoms of hypothyroidism include a low rate of metabolism with cold intolerance, lethargy, and weight gain. The features of hyperthyroidism are the opposite of hypothyroidism. Graves’ disease, weight loss, poor emotional control, and high blood pressure are symptoms of hyperthyroidism.

Capillary pressure and hydrostatic pressure are called Starling forces. Proteins of blood plasma pull fluid into the capillaries. This is called oncotic pressure. This pressure is much greater than the capillary hydrostatic pressure at the venule end of capillary.

All are true except D. Pepsinogen, which is produced by chief cells, is converted to pepsin by hydrochloric acid (HCl).

Secretin hormone is produced by the duodenum and stimulates the pancreas to secrete sodium bicarbonate for neutralizing acid chyme. Enterogastrone prohibits the gastric secretion.

All are true except E. The functions of the large intestine are the absorption of water and ions, storage of feces, and absorption of vitamin K, which is produced by harbor bacteria. There is no secretion of enzymes or hormones in the large intestine.

Renal system secretion is the transport of materials such as toxins and salts from peritubular capillary to renal tubule by active transport. Secretion and reabsorption function in regulation of salt and pH in body fluids. Descending or ascending loop of Henle is related to reabsorption, and high concentration of urea is related to excretion.

Endocrine glands, called ductless glands, secrete their products or hormones into the bloodstream. Exocrine glands secrete their products into ducts. Giantism is related to Growth Hormone (GH) in the anterior pituitary gland.

All are correct.

All are true except E. Animals cannot synthesize vitamins.

The cardiovascular system supplies oxygen and nutrients to body tissues and takes out wastes from the body. Heart, blood pressure, blood, and blood vessels are all necessary to transport these materials.

Pepsin secreted by the stomach begins to break down protein into small polypeptides. Salivary amylase starts to break down polysaccharides into disaccharides in the mouth. All of the above molecules can be digested in the small intestine.

The proximal tubule secretes and reabsorbs water, salts, and nutrients (glucose, amino acid). The descending loop of Henle reabsorbs water and the ascending loop of Henle reabsorbs NaCl. The distal tubule secretes and reabsorbs water and salts.

Alcohol and caffeine inhibit the release of ADH hormone, which functions in reabsorption of water, so people become dehydrated by this reaction. Aldosterone is a stress response hormone that increases blood pressure and breathing rates. PTH (parathyroid hormone) and calcitonin are hormones that regulate blood calcium levels. PTH increases the blood calcium levels, while calcitonin decreases the blood calcium levels.