Difficulty: Intermediate | Prerequisites: Chapters 4 (tissue types), 10 (muscle tissue), 12 and 15 (nervous system and ANS basics)
This final block covers the major organ systems that keep the body alive and reproducing. Chapter 19 is the heart: its anatomy, wall layers, the pericardium, and the electrical conduction pathway. Chapter 20 extends to the blood vessels, comparing arteries, veins, and capillaries. Chapter 22 covers the respiratory system from the nose to the alveoli. Chapter 23 maps the digestive tract and its accessory organs. Chapter 24 deals with the urinary system, centred on kidney anatomy and the nephron. Chapter 25 finishes with the reproductive systems. Each of these chapters is anatomy-heavy, asking you to identify structures and understand the tissue layers that compose them.
The heart has four chambers, three wall layers, and its own electrical conduction system. Blood vessels come in three types (arteries, veins, capillaries), each with a distinct wall structure. The respiratory tract splits into a conducting zone and a respiratory zone. The GI tract has four wall layers and is supported by accessory organs. Kidneys contain nephrons that filter blood. Male and female reproductive systems each have primary sex organs (gonads) and secondary sex organs.
Pericardium
A three-layered sac surrounding the heart. From outside in: fibrous pericardium (tough outer layer), parietal serous pericardium (lines the inside of the fibrous layer), visceral serous pericardium (also called the epicardium, directly on the heart surface). The pericardial cavity between the parietal and visceral layers contains a thin film of serous fluid.
Epicardium
The outermost layer of the heart wall. This is the visceral layer of the serous pericardium.
Myocardium
The thick middle layer of the heart wall. Composed of cardiac muscle, responsible for contraction.
Endocardium
The innermost layer of the heart wall. Lines the chambers and covers the valves. Composed of endothelium (simple squamous epithelium) and a thin layer of connective tissue.
Endothelium
Simple squamous epithelium that lines the interior of blood vessels and the heart. In simple terms, it is the slick inner lining that reduces friction as blood flows past.
Tunica intima
The innermost layer of a blood vessel wall. Composed of endothelium and a small amount of connective tissue.
Tunica media
The middle layer of a blood vessel wall. Composed of smooth muscle and elastic fibres. Thicker in arteries than in veins.
Tunica externa (adventitia)
The outermost layer of a blood vessel wall. Composed of fibrous connective tissue.
Conducting zone
The portion of the respiratory tract that filters, warms, and moistens incoming air but does not participate in gas exchange. Includes the nose, pharynx, larynx, trachea, bronchi, and bronchioles down to the terminal bronchioles.
Respiratory zone
The portion of the respiratory tract where gas exchange occurs. Includes respiratory bronchioles, alveolar ducts, and alveoli.
Alimentary canal (GI tract)
The continuous muscular tube from the mouth to the anus. Food passes through it during digestion.
Accessory digestive organs
Organs that assist digestion but are not part of the alimentary canal: teeth, tongue, salivary glands, liver, gallbladder, pancreas.
Peritoneum
A serous membrane lining the abdominal cavity (parietal peritoneum) and covering most abdominal organs (visceral peritoneum).
Mesentery
A double layer of peritoneum that anchors organs to the body wall and carries blood vessels, nerves, and lymphatics to the abdominal organs.
Nephron
The functional unit of the kidney. Each kidney contains roughly one million nephrons. Each nephron filters blood and produces urine.
Primary sex organs (gonads)
The organs that produce gametes and sex hormones. Testes in males, ovaries in females.
Secondary sex organs
All other reproductive structures: ducts, glands, and external genitalia that transport, nourish, or deliver gametes.
Gross structures
Four chambers: right atrium, right ventricle, left atrium, left ventricle
Atrioventricular (AV) valves: tricuspid (right side), bicuspid/mitral (left side); prevent backflow from ventricles to atria
Semilunar valves: pulmonary (right ventricle to pulmonary trunk), aortic (left ventricle to aorta); prevent backflow from great vessels into ventricles
External features: coronary sulcus, anterior interventricular sulcus, posterior interventricular sulcus; coronary arteries and veins
Layers of the heart wall
Epicardium (visceral serous pericardium): outermost
Myocardium: cardiac muscle, the bulk of the wall
Endocardium: endothelium lining the interior
Pericardium (three-layered sac)
Fibrous pericardium: tough, inelastic outer sac
Parietal serous pericardium: thin membrane lining the fibrous pericardium
Visceral serous pericardium (epicardium): on the heart's surface
Pericardial cavity with serous fluid sits between parietal and visceral layers
Electrical conduction pathway
SA node (sinoatrial node, the pacemaker) in the right atrium
Signal spreads across both atria
AV node (atrioventricular node) at the junction of atria and ventricles; brief delay here
AV bundle (bundle of His) through the interventricular septum
Right and left bundle branches down the septum
Purkinje fibres (subendocardial conducting network) spread the impulse through the ventricular walls
Blood flow through the heart
Deoxygenated blood: superior/inferior vena cava and coronary sinus → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary trunk → pulmonary arteries → lungs
Oxygenated blood: pulmonary veins → left atrium → mitral (bicuspid) valve → left ventricle → aortic valve → aorta → systemic circulation
Arteries versus veins versus capillaries
Arteries: carry blood away from the heart; thick walls with abundant smooth muscle and elastic tissue in the tunica media; withstand high pressure
Veins: carry blood toward the heart; thinner walls, larger lumens; contain valves to prevent backflow; rely on the skeletal muscle pump and respiratory pump to return blood
Capillaries: smallest vessels, one cell thick (endothelium only); site of gas, nutrient, and waste exchange between blood and tissues
Wall layers of arteries and veins
Tunica intima: endothelium (innermost)
Tunica media: smooth muscle and elastic fibres (much thicker in arteries)
Tunica externa: fibrous connective tissue (may be the thickest layer in veins)
Distinguishing arteries from veins histologically
Arteries: thicker tunica media, smaller lumen relative to wall thickness, more rounded in cross-section
Veins: thinner tunica media, larger lumen relative to wall thickness, often appear collapsed or irregular in cross-section
Why capillaries are "leaky"
Their walls are just a single layer of endothelium with a basement membrane
No tunica media, no tunica externa
Intercellular clefts (gaps between endothelial cells) allow fluid and small solutes to pass
Fenestrated capillaries have pores (fenestrations) that further increase permeability
This minimal wall structure is what allows exchange to occur
Venous valves and the skeletal muscle pump
Veins, especially in the limbs, contain one-way valves that prevent blood from pooling due to gravity
The skeletal muscle pump: when surrounding skeletal muscles contract, they compress veins and push blood toward the heart; valves ensure unidirectional flow
Conducting versus respiratory zone
Conducting zone: nose, pharynx, larynx, trachea, bronchi, bronchioles (to terminal bronchioles); filters, warms, humidifies air; no gas exchange
Respiratory zone: respiratory bronchioles, alveolar ducts, alveoli; where gas exchange occurs
Paranasal sinuses
Air-filled cavities in the frontal, sphenoid, ethmoid, and maxillary bones
Lighten the skull and warm/moisten inhaled air
Olfactory versus respiratory mucosae
Olfactory mucosa: lines the superior nasal cavity; contains olfactory receptors for smell
Respiratory mucosa: lines most of the nasal cavity and much of the conducting zone; pseudostratified ciliated columnar epithelium with goblet cells that traps and moves debris
Pharynx (three divisions)
Nasopharynx: posterior to the nasal cavity, above the soft palate; air passage only
Oropharynx: posterior to the oral cavity; shared passage for food and air
Laryngopharynx: inferior portion, opens into the larynx and oesophagus
Larynx
Houses the vocal folds (true vocal cords, which vibrate to produce sound) and the vestibular folds (false vocal cords, which do not produce sound but protect the true folds)
Composed of cartilages including the thyroid cartilage, cricoid cartilage, and epiglottis
Trachea
C-shaped rings of hyaline cartilage keep the airway open
The open part of the C faces posteriorly, where the trachealis muscle (smooth muscle) and the oesophagus sit
Lined by pseudostratified ciliated columnar epithelium (respiratory mucosa)
Alveoli and respiratory membrane
Alveoli are tiny air sacs where gas exchange occurs
The respiratory membrane consists of the alveolar epithelium (type I alveolar cells, simple squamous), the fused basement membranes, and the capillary endothelium
This membrane is extremely thin, allowing rapid diffusion of O₂ and CO₂
Lungs and bronchial tree
Right lung: three lobes (superior, middle, inferior)
Left lung: two lobes (superior, inferior); contains the cardiac notch
Bronchial tree: trachea → primary (main) bronchi → secondary (lobar) bronchi → tertiary (segmental) bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveoli
Alimentary canal versus accessory organs
Alimentary canal: mouth, pharynx, oesophagus, stomach, small intestine, large intestine, anus
Accessory organs: teeth, tongue, salivary glands, liver, gallbladder, pancreas
Abdominal quadrants
Right upper quadrant (RUQ): liver, gallbladder, right kidney, portions of stomach and intestines
Left upper quadrant (LUQ): stomach, spleen, left kidney, pancreas (tail)
Right lower quadrant (RLQ): appendix, cecum, right ovary/ureter
Left lower quadrant (LLQ): descending colon, sigmoid colon, left ovary/ureter
Four layers of the GI tract wall (from lumen outward)
Mucosa: innermost; epithelium, lamina propria (loose CT), muscularis mucosae (thin smooth muscle)
Submucosa: dense connective tissue with blood vessels, nerves (submucosal plexus)
Muscularis externa: two layers of smooth muscle (inner circular, outer longitudinal); responsible for peristalsis
Serosa (or adventitia): outermost; visceral peritoneum where the organ is intraperitoneal; adventitia (fibrous CT) where retroperitoneal
Peritoneum and mesentery
Peritoneum: serous membrane with parietal (lines cavity wall) and visceral (covers organs) layers
Mesentery: double fold of peritoneum suspending organs and carrying their blood supply
Salivary glands
Parotid glands: anterior to the ears; largest; produce watery (serous) secretion
Submandibular glands: beneath the floor of the mouth
Sublingual glands: beneath the tongue; smallest; produce primarily mucous secretion
Oesophagus
Located posterior to the trachea
Muscular composition changes along its length: upper third is skeletal muscle, middle third is mixed, lower third is smooth muscle
Stomach
Regions: cardia, fundus, body, pylorus
Internal features: rugae (folds of the mucosa), gastric pits leading to gastric glands
Muscularis externa has three layers of smooth muscle (oblique, circular, longitudinal) rather than the usual two
Small intestine
Three divisions: duodenum (shortest, receives bile and pancreatic juice), jejunum (middle, primary site of nutrient absorption), ileum (longest, ends at the ileocecal valve)
Main digestive function: chemical digestion and absorption of nutrients
Large intestine
Regions: cecum (with appendix), ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anal canal
Main functions: water and electrolyte absorption, formation and storage of faeces, some vitamin production by bacteria
Distinctive features: teniae coli (three bands of longitudinal muscle), haustra (pouches), epiploic appendages (fat-filled peritoneal pouches)
Liver and gallbladder
Liver: largest internal organ; four lobes (right, left, caudate, quadrate); produces bile; receives blood from the hepatic artery and portal vein
Gallbladder: stores and concentrates bile; releases it into the duodenum via the cystic duct and common bile duct
Pancreas
Located retroperitoneally, posterior to the stomach
Head (nestled in the curve of the duodenum), body, tail
Exocrine function: produces pancreatic juice (digestive enzymes and bicarbonate) delivered to the duodenum
Endocrine function: pancreatic islets secrete insulin and glucagon (not a primary focus in this anatomy-based exam, but worth knowing)
Location of the kidneys
Retroperitoneal, flanking the vertebral column at approximately T12-L3
The right kidney sits slightly lower than the left due to the liver above it
Gross and internal anatomy of the kidneys
External: renal hilum (where vessels, ureter, and nerves enter/exit), surrounded by renal capsule (fibrous), perirenal fat, and renal fascia
Internal (frontal section): renal cortex (outer region), renal medulla (inner region, containing renal pyramids), renal columns (cortical tissue between pyramids), renal pelvis (funnel-shaped chamber continuous with the ureter), major and minor calyces (cup-shaped structures collecting urine from the pyramids)
Nephron
The functional unit of the kidney
Parts: renal corpuscle (glomerulus + Bowman's capsule), proximal convoluted tubule (PCT), loop of Henle (descending and ascending limbs), distal convoluted tubule (DCT)
The DCT empties into a collecting duct, which drains into the renal pelvis
Location: the renal corpuscle and convoluted tubules are in the cortex; the loop of Henle dips into the medulla
Ureters, urinary bladder, and urethra
Ureters: muscular tubes carrying urine from the renal pelvis to the bladder; retroperitoneal
Urinary bladder: a muscular reservoir for urine; wall contains the detrusor muscle (smooth muscle); the trigone is a smooth triangular area on the internal floor, defined by the two ureteral openings and the internal urethral orifice
Urethra: carries urine from the bladder to the exterior
Female urethra: short (approximately 3-4 cm), opens at the external urethral orifice anterior to the vaginal opening
Male urethra: longer (approximately 20 cm), passes through the prostate gland and the penis; serves as a shared pathway for urine and semen
Primary versus secondary sex organs
Primary sex organs (gonads): testes (male), ovaries (female); produce gametes (sperm, oocytes) and sex hormones
Secondary sex organs: ducts, glands, and external genitalia that transport, support, or deliver gametes
Male reproductive anatomy
Testes: produce sperm and testosterone; located in the scrotum
Epididymis: coiled tube on the posterior surface of the testis where sperm mature and are stored
Spermatic cord: contains the ductus (vas) deferens, testicular artery and veins, nerves, lymphatics, and the cremaster muscle
Pathway of sperm: seminiferous tubules (in testis) → epididymis → ductus (vas) deferens → ejaculatory duct → urethra (prostatic → membranous → spongy) → external urethral orifice
Penis: root (attached to the pelvis), shaft (body), glans (expanded distal end)
Female reproductive anatomy
Ovaries: produce oocytes and oestrogen/progesterone; located in the pelvic cavity, flanking the uterus
Uterine (Fallopian) tubes: transport the oocyte from the ovary toward the uterus; usual site of fertilisation; parts include the infundibulum (with fimbriae), ampulla, isthmus
Uterus: parts are the fundus (dome-shaped top), body (main portion), cervix (narrow inferior opening into the vagina)
Vagina: fibromuscular canal from the cervix to the exterior; lined by stratified squamous epithelium; serves as the birth canal and receives the penis during intercourse
Vulva (external genitalia): mons pubis, labia majora, labia minora, clitoris, vestibule (contains the vaginal and urethral openings)
Students sometimes think arteries always carry oxygenated blood. Pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs. The defining feature of an artery is that it carries blood away from the heart, regardless of oxygen content.
The conducting zone does not exchange gases. Students sometimes assume that because air passes through the trachea and bronchi, gas exchange happens there. It does not; exchange occurs only in the respiratory zone (alveoli and respiratory bronchioles).
The oesophagus is not entirely smooth muscle. Its upper third is skeletal muscle, the middle third is mixed, and only the lower third is smooth muscle. This transition matters because swallowing begins as a voluntary action and becomes involuntary.
Students often confuse the peritoneum with the mesentery. The peritoneum is the serous membrane itself; the mesentery is a specific double fold of peritoneum that anchors organs and carries vessels.
⚠️ Blood flow through the heart is a classic sequence question. Know the path from the venae cavae all the way through to the aorta, naming every chamber and valve in order.
⚠️ Be able to distinguish arteries from veins on a histological image. Look at the tunica media thickness and the lumen shape.
⚠️ The cardiac conduction pathway (SA node → atria → AV node → bundle of His → bundle branches → Purkinje fibres) is frequently tested as a sequence.
⚠️ Know the four layers of the GI tract wall from innermost to outermost: mucosa, submucosa, muscularis externa, serosa.
⚠️ Nephron anatomy, including which parts are in the cortex versus the medulla, is a reliable exam topic.
⚠️ The pathway of sperm from testis to external urethral orifice is another ordered-sequence question.
⚠️ Know that the vagina is lined by stratified squamous epithelium (a protective, abrasion-resistant lining).
True or false: The SA node is located in the left atrium.
Fill in the blank: Capillaries are composed of a single layer of __________ and a basement membrane.
True or false: The respiratory zone includes the trachea and primary bronchi.
Fill in the blank: The four layers of the GI tract wall, from lumen outward, are mucosa, submucosa, muscularis externa, and __________.
True or false: The renal corpuscle is located in the renal medulla.
Answers: 1. False (the SA node is in the right atrium). 2. Endothelium (simple squamous epithelium). 3. False (those are part of the conducting zone; the respiratory zone begins at the respiratory bronchioles). 4. Serosa (or adventitia). 5. False (the renal corpuscle is in the cortex).
Q: Name the three layers of the heart wall from outermost to innermost.
A: Epicardium (visceral serous pericardium), myocardium (cardiac muscle), endocardium (endothelial lining).
Q: Trace the path of blood flow through the heart, starting from the venae cavae.
A: Superior/inferior vena cava → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary trunk → pulmonary arteries → lungs → pulmonary veins → left atrium → mitral (bicuspid) valve → left ventricle → aortic valve → aorta.
Q: What structural features make capillaries well suited for exchange?
A: Their walls are only one cell thick (endothelium + basement membrane), they lack tunica media and tunica externa, and many have intercellular clefts or fenestrations. This minimal barrier allows efficient diffusion of gases, nutrients, and wastes.
Q: What are the three divisions of the pharynx?
A: Nasopharynx, oropharynx, laryngopharynx.
Q: List the four layers of the GI tract wall from innermost to outermost and state the main component of each.
A: Mucosa (epithelium, lamina propria, muscularis mucosae), submucosa (dense connective tissue with vessels and nerves), muscularis externa (smooth muscle, inner circular and outer longitudinal layers), serosa or adventitia (visceral peritoneum or fibrous connective tissue).
Q: Describe the parts of the nephron and where each is located.
A: Renal corpuscle (glomerulus and Bowman's capsule) in the cortex; proximal convoluted tubule (PCT) in the cortex; loop of Henle descends into the medulla and returns to the cortex; distal convoluted tubule (DCT) in the cortex. The collecting duct runs through the medulla.
Q: Trace the pathway of sperm from production to exit.
A: Seminiferous tubules → epididymis → ductus (vas) deferens → ejaculatory duct → prostatic urethra → membranous urethra → spongy (penile) urethra → external urethral orifice.
The cardiac conduction system (Ch. 19) is regulated by the autonomic nervous system (Ch. 15): the sympathetic division increases heart rate, and the parasympathetic division (via the vagus nerve, Ch. 14) slows it.
Blood vessel histology (Ch. 20) relies on understanding the three tunics, which are built from the tissue types introduced in Chapter 4 (endothelium, smooth muscle, connective tissue).
The respiratory and digestive systems share the pharynx (Ch. 22, Ch. 23), and the vagus nerve (Ch. 14) innervates structures in both systems.
The urinary and reproductive systems share the urethra in males (Ch. 24, Ch. 25), which is why the male urethra is longer and has three named regions.
heart anatomy, heart chambers, heart valves, tricuspid, bicuspid, mitral, aortic valve, pulmonary valve, epicardium, myocardium, endocardium, pericardium, cardiac conduction, SA node, AV node, bundle of His, Purkinje fibres, blood flow through the heart, arteries, veins, capillaries, tunica intima, tunica media, tunica externa, endothelium, venous valves, skeletal muscle pump, respiratory system, conducting zone, respiratory zone, pharynx, nasopharynx, oropharynx, laryngopharynx, larynx, vocal folds, trachea, C-shaped cartilage, trachealis muscle, alveoli, respiratory membrane, bronchial tree, digestive system, alimentary canal, GI tract layers, mucosa, submucosa, muscularis externa, serosa, peritoneum, mesentery, salivary glands, oesophagus, stomach, small intestine, duodenum, jejunum, ileum, large intestine, colon, liver, gallbladder, pancreas, abdominal quadrants, urinary system, kidney anatomy, renal cortex, renal medulla, nephron, glomerulus, Bowman's capsule, PCT, loop of Henle, DCT, collecting duct, ureter, urinary bladder, urethra, reproductive system, testes, epididymis, spermatic cord, ductus deferens, sperm pathway, penis, ovaries, uterine tubes, uterus, vagina, vulva, stratified squamous epithelium, APK2100C, anatomy and physiology, UF