B Pharmacy Sem 2: Human Anatomy and Physiology II

Subject: Human Anatomy and Physiology II

1. 1. Cardiovascular & Lymphatic Systems
   2. Respiratory System
   3. Digestive System & Metabolism
   4. Urinary System & Fluid & Electrolyte Balance
   5. Endocrine Glands & Hormonal Regulation
   6. Reproductive System & Developmental Physiology

Unit 1: Cardiovascular & Lymphatic Systems

This unit covers the heart, blood vessels, blood, and lymphatic system. You’ll learn the structure and function of the heart, the cardiac cycle, blood circulation types, blood components, hemostasis, and lymphatic organs—essential for understanding drug distribution, pathology, and immune responses.

1.1 Heart Anatomy

The heart is a muscular, four-chambered pump that maintains blood circulation.

• Chambers: Right atrium, right ventricle, left atrium, left ventricle

• Valves: Tricuspid (RA–RV), pulmonary (RV–pulmonary artery), mitral/bicuspid (LA–LV), aortic (LV–aorta)

• Layers of Heart Wall:

  • Endocardium: inner lining

  • Myocardium: thick muscle layer

  • Epicardium: outer protective layer

• Pericardium: double-walled sac enclosing heart; pericardial fluid reduces friction.

1.2 Conducting System of the Heart

The heart has an intrinsic electrical system that coordinates contraction:

• SA Node (Sinoatrial Node): natural pacemaker; initiates impulse

• AV Node (Atrioventricular Node): delays impulse for ventricular filling

• Bundle of His: conducts impulse to ventricles

• Purkinje Fibers: spread impulse through ventricular myocardium

This system creates the cardiac cycle, a repeating sequence of systole (contraction) and diastole (relaxation).

1.3 Cardiac Cycle

• Atrial Systole: atria contract → ventricles fill

• Ventricular Systole: ventricles contract → blood ejected into aorta and pulmonary artery

• Diastole: both atria and ventricles relax → chambers refill

Heart sounds:

• S1 (“lub”): closure of AV valves

• S2 (“dub”): closure of semilunar valves

1.4 Blood Vessels & Circulation

• Arteries: carry blood away from heart (high pressure)

• Veins: return blood to heart (low pressure, valves prevent backflow)

• Capillaries: microscopic vessels for exchange of gases, nutrients, wastes

Circulatory pathways:

• Systemic circulation: LV → body → RA

• Pulmonary circulation: RV → lungs → LA

• Coronary circulation: supplies heart muscle

1.5 Blood

Blood is a fluid connective tissue (5–6 L in adults).

• Components:

  • Plasma (55%): water, proteins (albumin, globulin, fibrinogen), nutrients, hormones, waste products

  • Formed elements (45%):

    • Erythrocytes (RBCs): carry oxygen via hemoglobin

    • Leukocytes (WBCs): immune defense

    • Thrombocytes (platelets): blood clotting

1.6 Hemostasis & Blood Coagulation

Hemostasis stops bleeding after vessel injury:

1. Vascular spasm: immediate vasoconstriction

2. Platelet plug formation: platelets adhere and aggregate

3. Coagulation cascade: fibrin mesh forms clot

Intrinsic & Extrinsic pathways converge at factor X → thrombin → fibrin.

1.7 Blood Groups

• ABO System: A, B, AB, O blood types based on antigen presence

• Rh factor: positive (+) or negative (–); important in transfusion and pregnancy

• Cross-matching: prevents transfusion reactions.

1.8 Lymphatic System

The lymphatic system drains tissue fluid (lymph) back to circulation, filters pathogens, and helps immunity.

• Lymph vessels: parallel veins, return lymph via thoracic duct & right lymphatic duct

• Lymph nodes: filter lymph, house lymphocytes

• Organs: spleen (filters blood), thymus (T-cell maturation), tonsils (first defense in oral/nasal cavities)

Functions:

• Maintain fluid balance

• Absorb fats from intestine (lacteals)

• Provide immune surveillance

1.9 Clinical Correlations

• Hypertension: sustained high blood pressure; risks heart attack, stroke

• Atherosclerosis: plaque buildup in arteries; leads to coronary artery disease

• Anemia: reduced RBCs/hemoglobin; causes fatigue, pallor

• Leukemia: cancer of WBCs; abnormal proliferation

• Lymphedema: lymphatic blockage; swelling of tissues

1.10 Key Points for Exams

✔ Be able to label heart chambers and valves
✔ Explain cardiac cycle phases and heart sounds
✔ List blood components and their functions
✔ Describe hemostasis steps
✔ Understand ABO/Rh blood grouping
✔ Recall major lymphatic organs and their roles

Unit 2: Respiratory System

This unit explores the structures and functions of the respiratory tract, the mechanics of breathing, pulmonary volumes and capacities, gas exchange and transport, and neural and chemical regulation of respiration.

2.1 Anatomy of the Respiratory Tract

• Upper Respiratory Tract:

  • Nasal cavity & sinuses: filter, warm and humidify inspired air

  • Pharynx & larynx: conduct air; larynx houses vocal cords

• Lower Respiratory Tract:

  • Trachea: C‑shaped cartilaginous rings maintain patency

  • Bronchi & bronchioles: branching network; terminal bronchioles lead to respiratory zone

  • Alveoli: thin‑walled sacs for gas exchange; Type I (structure) and Type II (surfactant secretion) pneumocytes

2.2 Mechanics of Breathing (Pulmonary Ventilation)

Breathing depends on pressure differences between alveoli and atmosphere:

• Inspiration (active):

  • Diaphragm contracts (flattens)

  • External intercostals elevate ribs

  • Intrapulmonary pressure ↓ → air flows in

• Expiration (passive at rest):

  • Diaphragm and intercostals relax

  • Elastic recoil ↑ intrapulmonary pressure → air expelled

• Forced breathing uses accessory muscles (sternocleidomastoids, abdominals).

2.3 Lung Volumes & Capacities

Measured by spirometry to assess pulmonary function:

2.4 Gas Exchange & Transport

• External Respiration:

  • Alveolar gas exchange across respiratory membrane (thin barrier)

  • Fick’s law: rate ∝ surface area × pressure gradient ÷ thickness

• Internal Respiration:

  • Exchange of O₂ and CO₂ between blood and tissues

• O₂ Transport:

  • ~98 % bound to hemoglobin (forms oxyhemoglobin)

  • ~2 % dissolved in plasma

• CO₂ Transport:

  • ~70 % as bicarbonate (HCO₃⁻)

  • ~23 % bound to hemoglobin (carbaminohemoglobin)

  • ~7 % dissolved

• Oxyhemoglobin Dissociation Curve: factors shifting curve:

  • Right shift (↓ pH, ↑ CO₂, ↑ temperature) promotes O₂ release

  • Left shift (↑ pH, ↓ CO₂, ↓ temperature) promotes O₂ binding

2.5 Regulation of Respiration

• Neural Control:

  • Medullary respiratory centers: dorsal (inspiration), ventral (expiration)

  • Pontine centers: fine‑tune rhythm

• Chemical Control:

  • Central chemoreceptors (medulla): respond to ↑ PCO₂ (via H⁺)

  • Peripheral chemoreceptors (carotid & aortic bodies): respond to ↓ PO₂, ↑ PCO₂, ↓ pH

• Other Influences:

  • Stretch reflexes (Hering–Breuer) prevent over‑inflation

  • Higher brain centers (voluntary control, emotions)

2.6 Clinical Correlations

• Asthma: chronic bronchoconstriction, inflammation; measured by ↓ FEV₁/ FVC ratio

• Chronic Obstructive Pulmonary Disease (COPD): emphysema + chronic bronchitis; ↑ RV, ↓ VC

• Acute Respiratory Distress Syndrome (ARDS): increased alveolar membrane permeability → hypoxemia

• Pneumonia: alveolar fluid/inflammation impairs gas exchange

• Hypoxia Types: hypoxemic, anemic, circulatory, histotoxic

2.7 Key Points for Exams

• Be able to draw and label respiratory volumes and capacities

• Explain mechanics of inspiration and expiration

• Describe gas exchange mechanisms and O₂/CO₂ transport

• Know factors that shift the oxyhemoglobin dissociation curve

• Recall neural vs. chemical controls of breathing

• Recognize basic spirometric patterns in obstructive vs. restrictive diseases

Unit 3: Digestive System & Metabolism

This unit examines the structure and function of the gastrointestinal (GI) tract, accessory organs, digestive secretions, mechanisms of nutrient digestion and absorption, and key metabolic pathways that transform food into usable energy and biomolecules.

3.1 Anatomy of the Gastrointestinal Tract

• Alimentary Canal (mouth → anus):

  • Mouth & Pharynx: ingestion, mastication, bolus formation

  • Esophagus: muscular tube; peristalsis transports bolus

  • Stomach: storage; mechanical churning and acid–pepsin digestion

  • Small Intestine (duodenum, jejunum, ileum): primary site of digestion and absorption

  • Large Intestine (cecum, colon, rectum): water absorption, feces formation

• Accessory Organs:

  • Salivary Glands: secrete amylase‑rich saliva

  • Liver: produces bile for fat emulsification

  • Gallbladder: concentrates and stores bile

  • Pancreas: exocrine (digestive enzymes, bicarbonate) and endocrine (insulin, glucagon) functions

3.2 Digestive Secretions & Enzymes

3.3 Mechanisms of Digestion & Absorption

• Carbohydrates: starch → maltose (amylases) → monosaccharides (glucose, galactose, fructose) via brush‑border enzymes; absorbed by secondary active transport (SGLT) and facilitated diffusion (GLUT).

• Proteins: pepsin in stomach; trypsin/chymotrypsin → small peptides; brush‑border peptidases → amino acids; absorbed via active transport.

• Lipids: emulsified by bile salts → micelles; lipases → monoglycerides + free fatty acids; re‑esterified to triglycerides in enterocytes; packaged into chylomicrons for lymphatic transport.

• Vitamins & Minerals:

  • Fat‑soluble (A, D, E, K) with fats via micelles

  • Water‑soluble (B‑complex, C) by diffusion or transporters

  • Minerals (e.g., Ca²⁺ by vitamin D–dependent active transport; Fe²⁺ via DMT1)

3.4 Blood Supply & Portal Circulation

• Arterial Supply: celiac trunk, superior and inferior mesenteric arteries

• Portal System: nutrient‑rich blood from GI tract → hepatic portal vein → liver sinusoids for detoxification and metabolism → hepatic veins → systemic circulation

3.5 Overview of Metabolism

• Anabolic vs. Catabolic Pathways:

  • Catabolism: breakdown of macronutrients to generate ATP

  • Anabolism: synthesis of complex molecules (glycogen, fatty acids, proteins) using ATP

• Key Pathways:

  • Glycolysis (cytosol): glucose → 2 pyruvate + 2 ATP + 2 NADH

  • Pyruvate Dehydrogenase Complex (mitochondria): pyruvate → acetyl‑CoA + NADH + CO₂

  • Citric Acid Cycle (mitochondria): acetyl‑CoA → CO₂ + 3 NADH + FADH₂ + GTP

  • Electron Transport Chain & Oxidative Phosphorylation (inner mitochondrial membrane): NADH/FADH₂ → ATP (≈ 34 ATP per glucose)

  • Gluconeogenesis: non‑carbohydrate → glucose (liver, kidney)

  • Glycogenesis & Glycogenolysis: glucose ↔ glycogen (storage and mobilization)

3.6 Regulation of Metabolism

• Hormonal Control:

  • Insulin: secreted by β‑cells in response to ↑ blood glucose; promotes uptake and storage (glycogenesis, lipogenesis, protein synthesis)

  • Glucagon: secreted by α‑cells when glucose low; stimulates glycogenolysis and gluconeogenesis

  • Epinephrine & Cortisol: stress hormones; mobilize energy stores (glycogenolysis, lipolysis)

• Allosteric & Covalent Regulation:

  • Phosphofructokinase‑1 (PFK‑1): key glycolysis control (activated by AMP, fructose‑2,6‑bisphosphate; inhibited by ATP, citrate)

  • Glycogen Phosphorylase: regulated by phosphorylation (activated by glucagon/epinephrine via PKA)

3.7 Clinical Correlations

• Peptic Ulcer Disease: erosion of mucosa by excess HCl or H. pylori infection

• Malabsorption Syndromes: celiac disease, pancreatic insufficiency → nutrient deficiencies

• Jaundice: hyperbilirubinemia due to impaired bile flow or liver disease

• Diabetes Mellitus: Type 1 (insulin deficiency) and Type 2 (insulin resistance) disrupt glucose homeostasis

• Inborn Errors of Metabolism: e.g., phenylketonuria (phenylalanine hydroxylase deficiency)

3.8 Key Points for Exams

• Identify regions of the GI tract and major accessory organs

• List digestive enzymes and their sources/actions

• Describe absorption mechanisms for carbs, proteins, and fats

• Outline major metabolic pathways (glycolysis, TCA cycle, etc.) and their net ATP yields

• Understand hormonal regulation of fuel metabolism

• Recognize clinical manifestations of digestive and metabolic disorders

Unit 4: Urinary System & Fluid & Electrolyte Balance

This unit covers the anatomy and function of the kidneys and urinary tract, mechanisms of urine formation, compartments of body fluid, and the homeostatic regulation of water and key electrolytes.

4.1 Anatomy of the Urinary System

• Kidneys

  • Location: retroperitoneal, T12–L3 level

  • External Regions: cortex (outer), medulla (inner pyramids), pelvis (collecting funnel)

  • Blood Supply: renal artery → segmental → interlobar → arcuate → cortical radiate arteries; venous return via matching veins

• Ureters: muscular tubes conveying urine from renal pelvis to bladder via peristalsis

• Urinary Bladder: distensible storage; detrusor muscle; trigone region sensitive to stretch

• Urethra: conveys urine out; sphincters (internal involuntary, external voluntary)

4.2 The Nephron: Functional Unit

• Components

  • Renal Corpuscle: glomerulus (capillary tuft) + Bowman’s capsule

  • Renal Tubule:

    • Proximal Convoluted Tubule (PCT)

    • Loop of Henle (descending & ascending limbs)

    • Distal Convoluted Tubule (DCT)

    • Collecting Duct (cortical → medullary)

• Nephron Types

  • Cortical Nephrons (85 %): short loops, primarily for solute reabsorption

  • Juxtamedullary Nephrons (15 %): long loops, create medullary osmotic gradient for urine concentration

4.3 Mechanisms of Urine Formation

4.3.1 Glomerular Filtration

• Filtration Barrier: fenestrated endothelium + basement membrane + podocyte slits

• Forces (Starling’s):

  • Glomerular hydrostatic pressure (~55 mm Hg) ↑ filtration

  • Capsular hydrostatic pressure (~15 mm Hg) ↓

  • Oncotic pressure (~30 mm Hg) ↓

• Glomerular Filtration Rate (GFR): ~125 mL/min; regulated by afferent/efferent arteriole tone

4.3.2 Tubular Reabsorption

4.3.3 Tubular Secretion

• Active transport of H⁺, K⁺, organic acids/bases into tubule for excretion

4.3.4 Excretion

• Urine Output = Filtration – Reabsorption + Secretion

• Typical volume: 1–2 L/day; osmolarity: 50–1,200 mOsm/kg

4.4 Body Fluid Compartments & Water Balance

• Total Body Water ~60 % of body weight (42 L in 70 kg adult)

  • Intracellular Fluid (ICF) ~40 % (28 L)

  • Extracellular Fluid (ECF) ~20 % (14 L):

    • Plasma (~3 L)

    • Interstitial Fluid (~11 L)

• Water Movement via osmotic gradients across cell membranes

• Regulation

  • Thirst mechanism (hypothalamic osmoreceptors)

  • Antidiuretic Hormone (ADH): increases water reabsorption in collecting ducts

  • Atrial Natriuretic Peptide (ANP): promotes water and Na⁺ excretion

4.5 Electrolyte Balance

4.6 Hormonal Control of Renal Function

• Renin–Angiotensin–Aldosterone System (RAAS)

  1. Decreased renal perfusion → juxtaglomerular cells release renin

  2. Renin converts angiotensinogen → angiotensin I → ACE → angiotensin II

  3. Angiotensin II: vasoconstriction, stimulates aldosterone release → ↑ Na⁺/H₂O retention

• Antidiuretic Hormone (ADH)

  • Released by posterior pituitary in response to ↑ plasma osmolarity

  • Inserts aquaporin‑2 channels in collecting duct → ↑ water reabsorption

• Atrial Natriuretic Peptide (ANP)

  • Secreted by atrial myocytes in response to ↑ atrial stretch

  • Inhibits renin, aldosterone, ADH → ↑ Na⁺ and water excretion

4.7 Clinical Correlations

• Acute Kidney Injury (AKI): abrupt GFR decline; prerenal, intrinsic, or postrenal causes

• Chronic Kidney Disease (CKD): progressive nephron loss; stages based on GFR

• Edema: excess interstitial fluid—cardiac, renal, or hepatic origin

• Electrolyte Disorders:

  • Hyponatremia: confusion, seizures (excess water or Na⁺ loss)

  • Hyperkalemia/Hypokalemia: arrhythmias, muscle weakness

  • Metabolic Acidosis/Alkalosis: pH disturbances due to renal or respiratory dysfunction

4.8 Key Points for Exams

• Label kidney regions and nephron segments

• Explain Starling forces in glomerular filtration

• Trace tubular reabsorption and secretion steps with major solutes

• Differentiate ICF vs. ECF compartments and regulatory mechanisms

• Describe RAAS, ADH, and ANP actions on fluid/electrolyte balance

• Recognize lab findings and presentations of renal and electrolyte disorders

Unit 5: Endocrine Glands & Hormonal Regulation

This unit explores the structure and function of major endocrine glands, the hormones they secrete, mechanisms of hormone action, feedback control loops, and clinical disorders arising from hormonal imbalances.

5.1 Overview of the Endocrine System

• Endocrine vs. Exocrine: endocrine glands secrete hormones into bloodstream; exocrine glands use ducts.

• Hormone Types:

  • Peptide/Protein (e.g., insulin, growth hormone)

  • Steroid (e.g., cortisol, aldosterone, sex steroids)

  • Amine (e.g., thyroid hormones, catecholamines)

• Mechanisms of Action:

  • Cell-surface receptors for peptide/amine hormones → second messengers (cAMP, IP₃/DAG)

  • Intracellular receptors for steroid/thyroid hormones → direct gene transcription

5.2 Hypothalamic–Pituitary Axis

• Feedback Loops:

  • Negative feedback: rising hormone levels inhibit upstream release (e.g., cortisol ↓ CRH/ACTH).

  • Positive feedback: less common (e.g., oxytocin surge during labor).

5.3 Thyroid Gland

• Anatomy: two lobes connected by isthmus; follicles lined with follicular cells.

• Hormones:

  • Thyroxine (T₄) & Triiodothyronine (T₃): regulate basal metabolic rate, growth, and development

  • Calcitonin: from parafollicular C‑cells; lowers blood Ca²⁺

• Synthesis Pathway: iodide uptake → oxidation & iodination of thyroglobulin → coupling to form T₃/T₄ → release.

• Regulation: TRH → TSH → ↑ thyroid hormone.

5.4 Adrenal Glands

| Medulla | Epinephrine & Norepinephrine | Fight-or-flight: ↑ HR, BP, blood glucose |

• Control: ACTH stimulates cortisol & androgens; renin–angiotensin controls aldosterone; sympathetic preganglionic fibers control medulla.

5.5 Pancreatic Islets

• Cell Types & Hormones:

  • α‑cells: glucagon → ↑ blood glucose (glycogenolysis, gluconeogenesis)

  • β‑cells: insulin → ↓ blood glucose (glycogenesis, uptake by muscle/adipose)

  • δ‑cells: somatostatin → inhibits insulin, glucagon, GH release

  • PP‑cells: pancreatic polypeptide → regulates exocrine secretions

• Regulation: blood glucose is primary stimulus; incretins (GLP‑1) enhance insulin release.

5.6 Other Endocrine Glands

• Parathyroid Glands:

  • Parathyroid Hormone (PTH): ↑ blood Ca²⁺ by bone resorption, ↑ renal Ca²⁺ reabsorption, activates vitamin D.

• Pineal Gland:

  • Melatonin: regulates circadian rhythms; secreted in darkness.

• Gonads:

  • Ovaries: estrogen & progesterone regulate menstrual cycle, secondary sexual traits

  • Testes: testosterone controls spermatogenesis, male characteristics

• Thymus (functional in childhood):

  • Thymosins: T‑cell maturation

5.7 Hormone Action & Signal Transduction

• Second Messenger Systems:

  • cAMP pathway (e.g., ACTH, glucagon)

  • IP₃/DAG pathway (e.g., GnRH, ADH via V1 receptors)

• Receptor Types: G‑protein–coupled, tyrosine kinase (insulin), intracellular nuclear receptors (steroid/thyroid)

• Amplification & Termination: enzyme cascades amplify signal; phosphodiesterases and receptor internalization terminate signals.

5.8 Clinical Correlations

• Hypo/Hyperpituitarism: pituitary adenomas can cause dwarfism, acromegaly, Cushing’s disease

• Thyroid Disorders:

  • Hypothyroidism (e.g., Hashimoto’s): fatigue, weight gain, cold intolerance

  • Hyperthyroidism (e.g., Graves’): weight loss, heat intolerance, exophthalmos

• Adrenal Disorders:

  • Addison’s Disease: cortisol/aldosterone deficiency → hypotension, hyperpigmentation

  • Cushing’s Syndrome: cortisol excess → central obesity, hypertension, hyperglycemia

• Diabetes Mellitus: Type 1 (β‑cell destruction) vs. Type 2 (insulin resistance); complications include neuropathy, nephropathy

• Hyperparathyroidism/Hypoparathyroidism: Ca²⁺ imbalance → bone fragility or tetany

5.9 Key Points for Exams

• Match each gland with its hormones and functions

• Describe feedback loops in the hypothalamic–pituitary axes

• Outline thyroid hormone synthesis and regulation

• Differentiate adrenal cortex vs. medulla hormones and controls

• Explain insulin vs. glucagon actions on blood glucose

• Know clinical features of major endocrine disorders

Unit 6: Reproductive System & Developmental Physiology

This unit examines the anatomy and physiology of the male and female reproductive systems, gamete formation, hormonal regulation of reproduction, pregnancy and parturition, and early developmental processes.

6.1 Anatomy of the Male Reproductive System

• Testes: paired oval glands housed in the scrotum; produce sperm and testosterone

• Seminiferous Tubules: site of spermatogenesis; supported by Sertoli cells (nourish germ cells, form blood‑testis barrier)

• Interstitial (Leydig) Cells: secrete testosterone under LH stimulation

• Duct System:

  • Epididymis: sperm maturation and storage

  • Vas Deferens: transports sperm during ejaculation

  • Ejaculatory Duct & Urethra: passage through prostate and penis

• Accessory Glands:

  • Seminal Vesicles: fructose, prostaglandins, coagulating proteins

  • Prostate Gland: alkaline fluid, citrate, enzymes

  • Bulbourethral (Cowper’s) Glands: mucus for lubrication

6.2 Anatomy of the Female Reproductive System

• Ovaries: paired glands in pelvic cavity; produce ova and secrete estrogen & progesterone

• Ovarian Follicles: contain oocytes; mature through primordial → primary → secondary → Graafian stages

• Fallopian (Uterine) Tubes: capture ovulated oocyte; site of fertilization

• Uterus:

  • Layers: endometrium (stratum functionalis & basalis), myometrium (smooth muscle), perimetrium

  • Phases: proliferative, secretory, menstrual

• Cervix: mucus secretion; barrier to pathogens

• Vagina: acidic environment; conduit for sperm and birth canal

• External Genitalia: labia majora/minora, clitoris, vestibular glands

6.3 Gametogenesis

• Spermatogenesis (in seminiferous tubules):

  1. Spermatogonia (2n) → mitotic divisions →

  2. Primary Spermatocytes (2n) → Meiosis I →

  3. Secondary Spermatocytes (1n) → Meiosis II →

  4. Spermatids (1n) → spermiogenesis → mature spermatozoa

• Oogenesis:

  • Begins prenatally: oogonia → primary oocytes (arrested in Prophase I)

  • At puberty: each menstrual cycle, one primary oocyte completes Meiosis I → secondary oocyte (arrested in Metaphase II) + first polar body

  • After fertilization: secondary oocyte completes Meiosis II → ovum + second polar body

6.4 Hormonal Regulation of Reproduction

• Hypothalamic–Pituitary–Gonadal Axis:

  • GnRH (hypothalamus) → FSH & LH (anterior pituitary)

• In Males:

  • FSH → Sertoli cells → support spermatogenesis, produce inhibin (– feedback on FSH)

  • LH → Leydig cells → testosterone production (– feedback on LH & GnRH)

• In Females:

  • Follicular Phase: FSH stimulates follicle growth & estrogen secretion

  • Mid‑cycle LH Surge: triggers ovulation

  • Luteal Phase: ruptured follicle forms corpus luteum → secretes progesterone (and estrogen) to prepare endometrium; inhibin reduces FSH

6.5 Menstrual Cycle

6.6 Pregnancy, Parturition & Lactation

• Fertilization & Implantation:

  • Occurs in ampulla of fallopian tube within 24 h of ovulation

  • Blastocyst implants in endometrium ~6–7 days post‑fertilization

• Hormonal Changes in Pregnancy:

  • hCG (from syncytiotrophoblast) maintains corpus luteum first 8–10 weeks

  • Estrogen & Progesterone (placenta) support uterine growth and inhibit myometrial contractions

  • Relaxin: softens cervix and pelvic ligaments

• Parturition (Childbirth):

  • ↑ estrogen:progesterone ratio → ↑ oxytocin receptors on uterus

  • Ferguson reflex: stretch of cervix → oxytocin release → uterine contractions

  • Positive feedback: contractions → more oxytocin

• Lactation:

  • Prolactin (anterior pituitary) stimulates milk synthesis

  • Oxytocin triggers milk ejection (let‑down reflex) via myoepithelial cell contraction

6.7 Early Developmental Physiology

• Gastrulation: formation of three germ layers (ectoderm, mesoderm, endoderm) around week 3

• Neurulation: neural tube formation from ectoderm (future CNS)

• Organogenesis: weeks 4–8; major organs begin to form

• Fetal Circulation: special shunts bypass lungs (foramen ovale, ductus arteriosus, ductus venosus)

• Birth Adaptations: clamping of umbilical cord, first breath → closure of shunts

6.8 Clinical Correlations

• Infertility: anovulation, tubal blockages, low sperm count/motility

• Polycystic Ovary Syndrome (PCOS): hyperandrogenism, irregular cycles, insulin resistance

• Ectopic Pregnancy: implantation outside uterus (often in fallopian tube)

• Pre‑eclampsia: hypertension & proteinuria after 20 weeks gestation

• Testicular Disorders: cryptorchidism, varicocele, testicular torsion

6.9 Key Points for Exams

• Label male/female reproductive organs and stages of follicle development

• Outline spermatogenesis vs. oogenesis, including arrest points

• Describe hormonal control of menstrual cycle and feedback mechanisms

• Explain pregnancy hormones, implantation timing, and parturition reflexes

• Recall germ layer formation and major embryonic milestones

• Recognize features of common reproductive disorders