Digestion, Lymph and Immunity, Hormones, Kidneys, Reproduction, and Blood Terms
Unit 1: Anatomy and Physiology. Lesson 7 of 60 in CBET Academy.
The remaining body systems, at the depth the exam asks: the organ, its job, and the one fact that gets tested.
The digestive tract, in order
Digestion is movement, secretion, chemical breakdown, and absorption.
- Mouth: chewing (mastication) increases surface area; salivary amylase starts on starch and lingual lipase on fat.
- Esophagus: the epiglottis covers the airway during swallowing; the lower esophageal sphincter keeps acid out of the esophagus.
- Stomach: grinds food and adds gastric acid (pH about 1.5 to 3.5) and proteases; the pyloric sphincter releases the resulting chyme slowly.
- Small intestine: duodenum (first section, most chemical digestion, receives bile and pancreatic enzymes), jejunum (absorbs sugars, amino acids, fatty acids), ileum (finishes absorption, recovers bile salts).
- Large intestine: reabsorbs water to form solid waste; hosts bacteria that make vitamin K.
Accessory organs: the liver (largest solid organ; makes bile, plasma proteins, and cholesterol; stores glucose as glycogen; converts ammonia to urea; clears drugs and toxins; regulates clotting), the gallbladder (stores and concentrates bile, releases it into the duodenum), and the pancreas (exocrine digestive enzymes into the duodenum; endocrine insulin and glucagon into the blood).
Lymphatic and immune systems
The lymphatic system drains interstitial fluid as lymph through vessels with valves, filters it in lymph nodes (concentrated in the neck, armpits, and groin), and returns it to the veins through lymphatic ducts. Lymphoid tissues: tonsils, the thymus (where T cells mature), the spleen (cleans blood of old cells and pathogens), and Peyer's patches in the small intestine. The immune system uses white cells and antibodies to avoid, detect, and eliminate infection; it does not filter toxins (the kidneys do that) and is not controlled by the hypothalamus.
Endocrine glands and feedback
Hormones travel in blood and act only on cells with matching receptors. The hypothalamus and pituitary form the control center. Glands to know: thyroid (metabolic rate), parathyroid (four small glands on the posterior of the thyroid's lateral lobes; raise blood calcium), adrenal cortex (cortisol, salt and sugar balance) and adrenal medulla (epinephrine), pancreatic islets (insulin lowers glucose, glucagon raises it), thymus, pineal (daily rhythms), and the gonads. Most regulation is negative feedback: rising glucose triggers insulin, which lowers glucose, which stops the trigger. Positive feedback amplifies (labor contractions). The pons is brain stem, not a gland.
The kidney, closer up
Each kidney has an outer renal cortex, inner renal medulla, and a renal pelvis that funnels urine into the ureter. About a million nephrons do the work: blood enters the glomerulus (a capillary tuft inside Bowman's capsule), where blood pressure drives filtration; the filtrate runs through tubules that reabsorb water, glucose, and ions, secrete wastes and hydrogen ions (adjusting pH), and send the rest to collecting ducts as urine. Urine leaves through the ureters, the bladder, and the urethra. Dialysis imitates the nephron with a membrane and dialysate.
Reproduction
Male: testes make sperm and testosterone; sperm mature in the epididymis, travel the vas deferens, and mix with fluids from the seminal vesicles, prostate, and bulbourethral glands. Hormones: FSH drives sperm production, LH drives testosterone. Female: ovaries make eggs and secrete estrogen and progesterone; the egg travels the fallopian tube, where fertilization occurs, and the embryo implants in the uterus; the vagina is the birth canal.
Blood terms that get confused
Hemoglobin is the iron-containing protein in red cells that carries oxygen. Hematocrit is the fraction of blood volume that is red cells (about 45 percent), measured by spinning a sample in a hematocrit centrifuge. An adult has about 5 liters (five quarts) of blood. White cell types: lymphocytes, neutrophils, monocytes, eosinophils, basophils. Red cells live about four months and have no nucleus.
Digestion, Lymph and Immunity, Hormones, Kidneys, Reproduction, and Blood Terms, explained slowly
The rest of the body, room by room
These systems are tested with one or two facts each, usually a function-to-organ match. Use the digestive tract as a conveyor belt with stations, the kidney as a filter plant, the endocrine system as a thermostat network, and the lymphatic system as the building's drainage.
The conveyor belt
station action enzyme or chemical mouth mastication; starch and fat digestion begin salivary amylase, lingual lipase esophagus swallowing; epiglottis guards the airway lower esophageal sphincter blocks reflux stomach grinding; protein digestion; storage gastric acid pH 1.5 to 3.5, proteases; pyloric sphincter meters chyme out duodenum first small-intestine section; chemical digestion; absorption begins receives bile and pancreatic enzymes jejunum absorbs sugars, amino acids, fatty acids ileum finishes absorption; reclaims bile salts large intestine reabsorbs water; forms solid waste resident bacteria make vitamin K
Accessory organs: liver (bile production, plasma proteins, cholesterol, glycogen storage, urea from ammonia, detoxification, clotting regulation, immune support), gallbladder (stores and concentrates bile; releases it to the duodenum), pancreas (exocrine enzymes; endocrine insulin and glucagon). Secretin and cholecystokinin are duodenal hormones, not gallbladder products.
Drainage and defense
Interstitial fluid enters lymph capillaries, becomes lymph, is filtered in nodes (neck, armpits, groin), and returns to the veins through ducts; valves and muscle contraction move it. Lymphoid tissue: tonsils (throat), thymus (T-cell school), spleen (blood cleaner), Peyer's patches (intestine). The immune system's job is to avoid, detect, and eliminate infection. Two things it does not do: filter toxins (kidneys) and make blood cells on hormonal command (the kidney's erythropoietin does that).
The thermostat network
gland secretes effect hypothalamus releasing hormones commands the pituitary pituitary growth and control hormones master gland thyroid thyroxine metabolic rate, growth parathyroid parathyroid hormone raises blood calcium; four glands on the posterior lateral lobes of the thyroid adrenal cortex cortisol, aldosterone sugar, salt, stress adrenal medulla epinephrine heart rate, blood sugar, vessel size pancreatic islets insulin, glucagon lower and raise blood glucose thymus thymosin immune maturation pineal melatonin daily rhythms gonads estrogen, progesterone, testosterone
Negative feedback: the response cancels the stimulus (insulin after a meal). Positive feedback: the response amplifies the stimulus (oxytocin in labor). The pons is part of the brain stem and secretes nothing.
The filter plant
structure role renal cortex outer layer; holds the glomeruli renal medulla inner layer; collecting ducts renal pelvis funnel to the ureter nephron (about a million) the working unit glomerulus in Bowman's capsule capillary tuft where blood pressure forces filtrate out proximal tubule reabsorbs water, glucose, ions distal tubule secretes wastes and hydrogen ions (pH control) collecting duct final concentration; urine to the pelvis ureter, bladder, urethra transport, storage, exit
Filtration is driven by blood pressure, not osmosis or muscle. Dialysis reproduces the membrane step.
Reproduction, in one table
male female testes: sperm and testosterone ovaries: eggs, estrogen, progesterone epididymis stores; vas deferens carries fallopian tube: fertilization happens here seminal vesicles, prostate, bulbourethral fluids uterus: implantation and gestation FSH drives sperm production; LH drives testosterone vagina: receives sperm, birth canal
Blood terms
Hemoglobin is the iron protein that binds oxygen inside red cells; hematocrit is the red-cell fraction of blood volume (about 45 percent), read after spinning a capillary tube; total volume is about 5 liters. White cells: lymphocytes, neutrophils, monocytes, eosinophils, basophils; platelets clot; plasma is the water and proteins.
How the exam asks it
- "The large intestine ___." Reabsorbs water into the body to form solid waste.
- "What does the gallbladder secrete into the GI tract?" Bile.
- "Where is the parathyroid gland?" On the lateral lobes of the thyroid, posterior aspect.
- "Insulin release falling as glucose falls is an example of?" Negative feedback.
- "Which does not produce hormones: pituitary, pons, pancreas, ovaries?" Pons.
- "The primary driver of filtration in the kidneys?" Blood pressure.
- "Which statement about hemoglobin is wrong?" That it is the ratio of red cells to blood volume (that is hematocrit).
- "Fertilization occurs in the?" Fallopian tubes.
What to memorize
- The conveyor belt in order with its enzymes and the pH of the stomach; duodenum first, jejunum second, ileum third; large intestine reabsorbs water.
- Liver makes bile, gallbladder stores it, pancreas makes insulin and enzymes.
- Lymph nodes filter; thymus, spleen, tonsils, Peyer's patches.
- Parathyroid raises calcium on the back of the thyroid; negative feedback stabilizes.
- Cortex, medulla, pelvis; glomerulus, Bowman's capsule; blood pressure filters.
- Fallopian tube fertilization; FSH and LH.
- Hemoglobin carries, hematocrit is the fraction, five liters.