Digestion, Nutrition & Reproduction

What are the two categories of organs in the digestive system?

1) GI tract organs — form a continuous tube (oral cavity, pharynx, esophagus,

stomach, small & large intestine, anus).

2) Accessory digestive organs — assist digestion (salivary glands, liver, pancreas, teeth, tongue, gallbladder).

What are the 6 general functions of the digestive system?

Ingestion (taking in food), Motility (muscular movement/mixing), Secretion (releasing enzymes/acid/bile), Digestion (breakdown of food), Absorption (transport into blood/lymph), Elimination (excreting waste).

Mechanical vs. chemical digestion?

Mechanical = physical breakdown w/o changing chemical structure (chewing, mixing). Chemical = enzymatic breakdown that changes chemical structure (requires enzymes).

What are the 4 tunics of the GI tract wall (inner→outer)?

Mucosa → Submucosa → Muscularis → Adventitia (or Serosa).

What are the 3 layers of the mucosa and their functions?

Epithelium (contacts lumen contents, varies by region), Lamina propria (areolar CT, allows absorption into vessels), Muscularis mucosae (thin smooth muscle that increases mixing/secretion release).

What does the submucosa contain?

Areolar/dense irregular CT, blood & lymph vessels, nerves, the submucosal nerve plexus, and MALT (e.g., Peyer patches in small intestine) that guards against microbes.

Describe the muscularis layer and its nerve plexus.

Inner circular layer (constricts lumen) + outer longitudinal layer (shortens tube); myenteric nerve plexus lies between them and controls contractions. Thickens at sphincters.

Peristalsis vs. mixing movements?

Peristalsis = directional, wave-like propulsion of contents. Mixing = back-and- forth motion (no direction) that blends contents with secretions.

Adventitia vs. serosa — what's the difference?

Both are areolar CT outer tunics. Adventitia is outside the peritoneal cavity (not covered by peritoneum); serosa is inside the peritoneal cavity and covered by visceral

peritoneum.

Enteric nervous system (ENS) vs. Autonomic nervous system (ANS) role in digestion?

ENS = submucosal + myenteric plexus; senses/coordinates local mixing & propulsion. ANS: parasympathetic promotes GI activity, sympathetic inhibits it.

Short reflex vs. long reflex?

Short reflex = local, ENS only, coordinates small GI segments. Long reflex = involves CNS sensory input and autonomic motor output; coordinates motility, secretion, and accessory organs.

Name 4 hormones that regulate digestion.

Gastrin, Secretin, Cholecystokinin (CCK), and Motilin.

What do baroreceptors and chemoreceptors detect in the GI tract?

Baroreceptors detect stretch of the GI wall; chemoreceptors monitor the chemical content of the lumen (e.g., pH, nutrients).

Parietal vs. visceral peritoneum?

Parietal peritoneum lines the abdominal wall; visceral peritoneum covers the organs. The peritoneal cavity between them holds lubricating peritoneal fluid.

Intraperitoneal vs. retroperitoneal organs (examples)?

Intraperitoneal (surrounded by visceral peritoneum): stomach, most small intestine, parts of large intestine. Retroperitoneal (outside parietal peritoneum): most duodenum, pancreas, ascending/descending colon, rectum.

Name the key mesenteries/ ligaments and their functions.

Greater omentum (covers/insulates/stores fat), Lesser omentum (connects stomach & duodenum to liver), Falciform ligament (attaches liver to abdominal wall), Mesentery proper (suspends small intestine), Mesocolon (attaches large intestine).

What are the two regions of the oral cavity?

Vestibule (space between gums/lips/ cheeks) and oral cavity proper (central to teeth, leads to oropharynx).

Name the 3 pairs of extrinsic salivary glands and their % contribution to saliva.

Parotid (25–30%, largest, near ear), Submandibular (60–70%, most saliva), Sublingual (3–5%, under tongue).

What does saliva contain and what are its functions?

99.5% water + salivary amylase, mucin, lysozyme. Functions: moistens food into a bolus, starts starch digestion, dissolves food for taste, cleanses mouth, inhibits bacteria.

How is salivary secretion regulated?

Controlled by salivary nuclei in the brainstem. Parasympathetic stimulation (from oral/gastric receptors or thoughts of food) increases watery saliva; sympathetic stimulation makes saliva more viscous.

What is mastication and why is it important?

Chewing — mechanically reduces food size, increases surface area for enzymes, promotes salivation; coordinated by teeth/ lips/tongue/cheeks/jaw via the mastication center (medulla/pons

What are the 4 main parts of a tooth?

Dentin (main hard mass), Enamel (hardest substance in body, covers crown), Pulp cavity (center, blood vessels/nerves), Cementum (covers root).

Match tooth types to their function.

Incisors = cutting/slicing; Canines = puncturing/tearing; Premolars & Molars = crushing/grinding.

What are the 3 phases of deglutition (swallowing)?

1) Voluntary phase (cerebral cortex forms bolus, moves it to oropharynx).

2) Pharyngeal phase (involuntary reflex; soft palate/uvula block nasopharynx, epiglottis covers larynx).

3) Esophageal phase (peristalsis moves bolus to stomach; sphincters relax then close).

What is GERD and reflux esophagitis?

Inflammation of the esophagus from acidic chyme refluxing upward, causing heartburn. Common in overweight people, smokers, after large meals, and with hiatal hernia.

What are the 4 regions of the stomach?

Cardia (entry from esophagus), Fundus (dome, superior), Body (largest region), Pylorus (funnel-shaped terminal region with pyloric sphincter into duodenum).

List the 5 stomach secretory cell types and their products.

Surface mucous cells (alkaline mucus), Mucous neck cells (less alkaline mucus), Parietal cells (HCl + intrinsic factor), Chief cells (pepsinogen + gastric lipase), G-cells (gastrin & somatostatin hormones).

What are the functions of HCl in the stomach?

Converts pepsinogen → pepsin, denatures proteins, kills microorganisms, and helps break down plant carbs/connective tissue.

What is intrinsic factor and why is it important?

Secreted by parietal cells; required for vitamin B12 absorption in the small intestine, which is needed to make normal red blood cells.

Describe gastric mixing vs. gastric emptying.

Mixing: mechanical digestion turning bolus into chyme. Emptying: peristaltic waves push chyme against the pyloric sphincter, which opens briefly to release small amounts into the duodenum (retropulsion sends the rest back).

Describe the 3 phases of gastric regulation.

Cephalic phase: triggered by thought/sight/ smell/taste of food via vagal stimulation (increases motility/secretion). Gastric phase: stretch + protein in stomach triggers gastrin release & gastric reflex (increases activity). Intestinal phase: acidic chyme in duodenum triggers CCK & secretin, which slow stomach motility/secretion.

What does gastrin do?

Increases stomach contraction and HCl release, constricts the pyloric sphincter

(slows emptying), and increases small intestine digestive activity.

What is a peptic ulcer and its most common cause?

Erosion of the stomach (gastric ulcer) or duodenum (duodenal ulcer) lining; most often caused by Helicobacter pylori infection; can cause pain, bleeding, perforation.

What are the 3 segments of the small intestine?

Duodenum (1st, mostly retroperitoneal, receives bile/pancreatic secretions),

Jejunum (middle, main site of chemical digestion/absorption), Ileum (final, joins

large intestine at ileocecal valve).

What 3 structures increase small intestine surface area?

Circular folds (slow chyme, increase area), Villi (finger-like mucosal projections with capillaries + lacteal), Microvilli (brush border on villi epithelial cells).

What is a lacteal?

A lymphatic capillary inside a villus that absorbs lipids and lipid-soluble vitamins that can't enter the bloodstream directly.

What do small intestine gland cells secrete?

Goblet cells → mucin; unicellular gland cells → enteropeptidase (activates

trypsinogen→trypsin); enteroendocrine cells → CCK & secretin; duodenal

(Brunner) glands → alkaline mucus protecting from acidic chyme.

Segmentation vs. peristalsis in the small intestine?

Segmentation: back-and-forth mixing of chyme with secretions (pacemaker cell- driven). Peristalsis: migrating waves that propel contents toward the large intestine (triggered by hormone motilin).

What is the gastroileal reflex?

Food entering the stomach triggers ileum contraction and relaxation of the ileocecal sphincter/cecum (CCK-mediated), moving contents into the cecum; sphincter then contracts to prevent backflow.

Trace the path of bile from the liver to the duodenum.

Left/right hepatic ducts → common hepatic duct → joins cystic duct (from gallbladder) → common bile duct → joins pancreatic duct at the hepatopancreatic ampulla → enters duodenum at the major duodenal papilla, regulated by the hepatopancreatic sphincter.

What is the main digestive function of the liver?

Producing bile (the liver makes NO digestive enzymes). Bile mechanically emulsifies fats.

What is bile made of?

Water, bicarbonate ions, bile salts, bile pigment (bilirubin), cholesterol, lecithin, and mucin.

Describe liver histology: hepatocytes, sinusoids, Kupffer cells.

Hepatocytes = liver cells arranged in hepatic lobules; hepatic sinusoids = leaky capillaries where portal venous & arterial blood mix and nutrients are absorbed; Kupffer cells (reticuloendothelial cells) = macrophages that clear debris from sinusoidal blood; bile canaliculi carry bile to bile ductules in the portal triad.

What is the portal triad?

A bile ductule, a branch of the hepatic portal vein, and a branch of the hepatic artery found together at the edge of each hepatic lobule.

What does the gallbladder do?

Stores, concentrates, and releases bile produced by the liver via the cystic duct into the common bile duct.

What are gallstones?

Condensations of cholesterol or calcium + bile salts in the gallbladder/biliary ducts; risk factors include female sex, obesity, age; can cause cholecystitis, pain especially after fatty meals.

What are the endocrine and exocrine functions of the pancreas?

Endocrine (islet cells): produce insulin & glucagon. Exocrine (acinar cells): produce pancreatic juice for digestion.

What does pancreatic juice contain?

Alkaline fluid with water, bicarbonate, pancreatic amylase (starch), pancreatic lipase (triglycerides), inactive proteases (trypsinogen, chymotrypsinogen, procarboxypeptidase), and nucleases.

How do CCK and secretin regulate accessory organs?

CCK (released when chyme has protein/ fat): stops stomach motility, stimulates gallbladder to release bile & pancreas to release enzyme-rich juice, relaxes hepatopancreatic sphincter. Secretin (released with acidic chyme): stimulates alkaline (HCO3-) secretion from liver/ pancreas, inhibits gastric secretion/motility.

What are the 3 major regions of the large intestine?

Cecum (blind pouch receiving chyme, has appendix) → Colon (ascending, transverse, descending, sigmoid) → Rectum → Anus.

What are teniae coli, haustra, and omental appendices?

Teniae coli = 3 longitudinal smooth muscle bands; Haustra = pouches created by teniae coli bunching the colon; Omental appendices = fat-filled pouches hanging off the colon.

Describe large intestine motility.

Peristalsis (weak/sluggish), Haustral churning (distension triggers contraction to move material), Mass movements (strong tenia coli-driven contractions 2-3x/day pushing feces toward rectum).

Gastrocolic reflex vs. defecation reflex?

Gastrocolic reflex: stomach distension triggers mass movement in colon.

Defecation reflex: rectal stretch → parasympathetic signal → rectum/colon contract, internal anal sphincter relaxes; external (voluntary) sphincter relaxation allows defecation.

Internal vs. external anal sphincter?

Internal = involuntary smooth muscle (parasympathetic control).

External = voluntary skeletal muscle (somatic nervous system control).

What do large intestine bacteria (microbiota) do?

Chemically break down remaining complex carbs, proteins, and lipids, and produce vitamins B and K, which are then absorbed.

List the enzymes that digest carbohydrates and where they act.

Salivary amylase (mouth, starch→partial starch) → Pancreatic amylase (SI, →oligosaccharides/maltose/glucose) → Brush border: dextrinase/glucoamylase, maltase (→glucose), lactase (→glucose+galactose), sucrase (→glucose+fructose).

Why are proteolytic enzymes secreted in inactive forms?

To prevent the enzymes from digesting the very cells (stomach/pancreas) that produce them; they are activated only once in the GI lumen.

List the protein-digesting enzymes and locations.

Stomach: Pepsin (activated from pepsinogen by HCl) → polypeptides. Small intestine (pancreatic): Trypsin, Chymotrypsin (→polypeptides), Carboxypeptidase (→amino acids from carboxy end). Brush border: Dipeptidase, Aminopeptidase (→amino acids).

What is emulsification and what causes it?

Mechanical breakdown of large fat globules into smaller droplets by amphipathic bile salts (+ lecithin), forming micelles — increases surface area for pancreatic lipase.

Describe lipid absorption after digestion.

Micelles deliver monoglycerides/fatty acids/ cholesterol into epithelial cells (bile salts stay in lumen, recycled). Fatty acids reattach to monoglycerides to reform triglycerides, which are packaged with cholesterol into chylomicrons, exocytosed, and absorbed into lacteals.

What enzymes digest nucleic acids and where?

Small intestine only: Deoxyribonuclease (DNA→deoxyribonucleotides) & Ribonuclease (RNA→ribonucleotides) from pancreas; brush border Phosphatase (nucleotide→nucleoside+phosphate) and Nucleosidase (nucleoside→base+sugar).

How is vitamin B12 absorbed?

B12 is large, so it requires intrinsic factor (from gastric parietal cells) and is absorbed in the small intestine via receptor-mediated endocytosis.

How is iron absorption regulated?

The liver hormone hepcidin inhibits iron absorption in the small intestine; when iron is low, hepcidin decreases, allowing more absorption.

What is cirrhosis of the liver?

Hepatocytes replaced by fibrous scar tissue, compressing blood vessels (portal hypertension) & bile ducts; caused by chronic alcoholism, hepatitis B/C, drugs/ toxins; symptoms include fatigue, jaundice, ascites.

What is pancreatic cancer and why is prognosis often poor?

Cancer usually of exocrine pancreatic cells; hard to detect early (no screening test, few early symptoms); late symptoms include abdominal pain, jaundice, weight loss.

Diverticulosis vs. diverticulitis?

Diverticulosis = small bulges (diverticula) in the intestinal lining, often from a low-fiber diet.

Diverticulitis = inflammation of diverticula, which can be life-threatening if they rupture.

Define nutrition and nutrients.

Nutrition = the study of how organisms obtain/use nutrients to grow and sustain life.

Nutrients = biomolecules, vitamins, minerals (and water) obtained through food that are needed for synthesis and energy.

Macronutrients vs. micronutrients?

Macronutrients (carbs, lipids, proteins) are needed in large daily amounts.

Micronutrients (vitamins & minerals) are needed in small amounts.

Essential vs. nonessential nutrients?

Essential nutrients must be obtained from the diet (absorbed via digestive system). Nonessential nutrients can be made by the body's own biochemical processes.

What is RDA (Recommended Daily Allowance)?

The established amount of each nutrient that must be obtained daily, set by federal agencies (originally the Food & Nutrition Board); used for food planning/labeling/ education, reviewed periodically.

What are the 3 structural classes of carbohydrates and give examples?

Monosaccharides (glucose, fructose, galactose), Disaccharides (sucrose, lactose, maltose), Polysaccharides (starch, cellulose/fiber, glycogen).

How are carbohydrates classified by dietary source?

Sugars, Starch, and Fiber.

What is fiber and why is it important even though it's not digested?

Fibrous plant/animal molecules that cannot be chemically digested/absorbed; adds bulk, stimulates peristalsis ('keeps you regular'), and lowers cholesterol.

What happens to sugars/starch after digestion?

Usually converted to glucose, the primary energy-supplying nutrient; glucose is nonessential since it can be made via gluconeogenesis from other monosaccharides.

What are the 4 types of lipids?

Triglycerides, Phospholipids, Steroids, and Eicosanoids.

Saturated vs. unsaturated vs. polyunsaturated fatty acids?

Saturated: no double bonds, solid at room temp (meat, dairy, coconut/palm oil).

Unsaturated: 1 double bond, liquid at room temp (olive/canola oil). Polyunsaturated: 2+ double bonds, liquid at room temp (soybean/corn/safflower oil).

What are the functions/sources of cholesterol?

Component of the plasma membrane; precursor for steroid hormones, bile salts, and vitamin D. Comes from diet or is made by the liver.

How many amino acids are essential vs. nonessential?

8 essential amino acids must come from diet; the other 12 can be synthesized by the body.

Complete vs. incomplete proteins?

Complete proteins have all essential amino acids (generally animal proteins).

Incomplete proteins lack some essential amino acids (generally plant proteins) — no storage of excess, so must be eaten regularly.

How can vegetarians/vegans obtain all essential amino acids?

By combining different plant protein sources (complementary proteins), not necessarily at the same meal but regularly over time.

Positive vs. negative nitrogen balance?

Positive = absorbing more nitrogen than excreted (growth, pregnancy, injury recovery). Negative = excreting more nitrogen than absorbed (blood loss, malnutrition) — can be fatal.

Water-soluble vs. fat-soluble vitamins?

Water-soluble (B vitamins, C): dissolve in water, easily absorbed, excess excreted in urine. Fat-soluble (A, D, E, K): dissolve in fat, absorbed in micelles, excess stored in fat — can become toxic in excess.

What are the functions of vitamins A, D, E, and K?

A = precursor of visual pigment retinal.

D = forms calcitriol, increases calcium absorption.

E = stabilizes/protects cell membranes.

K = needed for blood clotting protein synthesis

Essential vs. nonessential vitamins?

Essential vitamins must come from diet (e.g., vitamin C, A) — deficiency occurs if intake/absorption is impaired. Nonessential vitamins are cofactors the body produces/ recycles (e.g., NADH, FADH2).

Major minerals vs. trace minerals?

Major minerals: >100 mg/day needed (calcium, chloride, potassium, phosphorus, magnesium). Trace minerals: <100 mg/day needed (chromium, copper, iodine, iron, zinc). All minerals are essential.

What are the key functions of iron, calcium, sodium/potassium, iodine, and zinc?

Iron: binds O2 in hemoglobin, part of electron transport.

Calcium: bone/muscle contraction/clotting/neurotransmitter release.

Sodium/Potassium: resting membrane potential & action potentials. Iodine: makes thyroid hormone.

Zinc: protein synthesis & wound healing.

What causes iron deficiency and what are the symptoms?

Insufficient intake or blood loss; it's the most common nutritional deficiency.

Symptoms: fatigue, weakness, pale skin, cold sensitivity. Hepcidin (liver hormone) regulates intestinal iron absorption.

What is MyPlate?

A USDA visual guide showing the recommended proportions of food groups on a plate: fruits, vegetables, grains, protein, plus a dairy serving.

What information is on a nutrition food label?

Serving size, calories, total fat, cholesterol, sodium, carbohydrates, protein, vitamins/ minerals — helps with meal planning for both healthy individuals and special diets.

How is obesity measured, and what's a limitation of BMI?

By Body Mass Index (BMI) = weight(kg)/ height(m²), or by underwater weighing/ DEXA. Limitation: BMI doesn't measure actual body fat, so muscular people may show a high BMI without being overweight.

What defines the fed (absorptive) state?

The ~4-hour period after eating/digesting/ absorbing nutrients; glucose, triglyceride, and amino acid blood levels rise as nutrients are absorbed; blood glucose maintained 70–110 mg/dL.

What does insulin do during the fed state?

Released from pancreas w/ rising blood glucose. Stimulates liver/muscle to store glucose as glycogen (glycogenesis); stimulates adipose uptake of triglycerides + lipogenesis (inhibits lipolysis); increases amino acid uptake & protein synthesis (anabolism).

What defines the fasting (postabsorptive) state?

The time between meals when the body relies on stored nutrients to maintain homeostatic blood levels.

What does glucagon do during the fasting state?

Released from pancreas as blood glucose falls. Stimulates liver glycogenolysis

(glycogen→glucose) and gluconeogenesis, and stimulates adipose lipolysis

(triglyceride breakdown). No effect on amino acids/proteins.

What are the main categories of liver function?

Carbohydrate metabolism, protein metabolism, lipid metabolism, lipid

transport, and other functions (storage,drug detoxification, plasma protein

formation, bilirubin removal, bile formation).

How does the liver synthesize cholesterol?

Fatty acids enter hepatocytes and are broken into 2-carbon acetyl CoA units via beta-oxidation; Acetyl CoA → cholesterol. Synthesis decreases when dietary cholesterol intake is high (and vice versa).

What happens to cholesterol after it's made in the liver?

It's released into blood as VLDL, or converted into bile salts (90% reabsorbed

in the ileum, 10% lost in feces).

What are lipoproteins and how are they classified?

Lipids wrapped in protein for blood transport, classified by density: VLDL (most lipid) → LDL (less lipid) → HDL (least lipid).

Describe the role of VLDL and LDL (liver → tissues).

VLDL: assembled in liver, released into blood, delivers triglycerides to peripheral tissues (mainly adipose); once triglycerides are released it becomes LDL.

LDL: cholesterol-rich, delivers cholesterol to cells via LDL receptors & endocytosis; used for membranes/steroid hormone synthesis.

Describe the role of HDL (tissues → liver).

Formed in liver (empty), circulates and picks up excess cholesterol from peripheral tissues, carries it back to the liver where it's converted to bile salts. Known as 'good cholesterol.'