Endocrine System

Overview of the Endocrine System

The endocrine system is a collection of glands that secrete hormones directly into the bloodstream to regulate various body functions. It works closely with the nervous system to maintain homeostasis.

• Endocrine vs Nervous System: The endocrine system uses hormones for long-term regulation, while the nervous system uses electrical impulses for rapid, short-term responses.

• Homeostasis: Both systems help maintain internal balance, but the endocrine system is slower and longer-lasting.

Steroid vs Non-Steroid Hormones

• Steroid Hormones: Lipid-soluble, derived from cholesterol, can pass through cell membranes (e.g., testosterone, estrogen, cortisol).

• Non-Steroid Hormones: Water-soluble, include peptides and amines, bind to cell surface receptors (e.g., insulin, ADH, TSH).

Major Hormones, Glands, Targets, and Functions

Thyroid Disorders

• Goiter: Enlargement of the thyroid gland, often due to iodine deficiency.

• Hypothyroidism: Low thyroid hormone levels; symptoms include fatigue, weight gain.

• Hyperthyroidism: Excess thyroid hormone; symptoms include weight loss, rapid heartbeat.

Thyroid Panel Blood Test

• Measures TRH, TSH, T3, T4, and assesses iodine's role in hormone synthesis.

Diabetes Mellitus

• Type I: Insulin-dependent; autoimmune destruction of β-cells.

• Type II: Insulin resistance; often associated with obesity.

Blood System

Components of Blood

• Whole Blood: Includes plasma and formed elements.

• Plasma: Liquid matrix; contains water, proteins, nutrients, hormones.

• Formed Elements: Erythrocytes (RBCs), leukocytes (WBCs), platelets.

Functions of Blood

• Transport of gases, nutrients, wastes, hormones.

• Regulation of pH, temperature, fluid volume.

• Protection against blood loss and infection.

Red Blood Cells (RBCs)

• Biconcave, anucleate cells specialized for oxygen transport via hemoglobin.

White Blood Cells (WBCs)

• Defend against pathogens; include neutrophils, lymphocytes, monocytes, eosinophils, basophils.

Complete Blood Count (CBC) with Differential

• Measures numbers and types of blood cells; helps diagnose diseases.

Types of Anemia

Erythropoietin (EPO)

• Hormone from kidneys stimulating RBC production in response to hypoxia.

Blood Typing

• ABO System: Based on presence of A/B antigens.

• Rh Factor: Presence (+) or absence (−) of D antigen.

Erythroblastosis Fetalis

• Hemolytic disease of the newborn due to Rh incompatibility.

Cardiovascular System: Heart

Heart Anatomy and Circulation

• Four chambers: right/left atria, right/left ventricles.

• Valves: tricuspid, pulmonary, mitral, aortic.

• Pulmonary Circulation: Right heart to lungs and back.

• Systemic Circulation: Left heart to body and back.

Heart as a Double Pump

• Right side pumps deoxygenated blood to lungs; left side pumps oxygenated blood to body.

Heart Sounds and Murmurs

• "Lub" (S1): AV valves closing.

• "Dub" (S2): Semilunar valves closing.

• Murmurs: Abnormal sounds due to valve defects.

Cardiac Pathologies

• CAD/CHD: Coronary artery disease/heart disease due to atherosclerosis.

• Myocardial Infarction: Heart attack; tissue death from blocked artery.

• Angina Pectoris: Chest pain from reduced blood flow.

• Cardiac Arrest: Sudden loss of heart function.

Treatments

• Balloon Angioplasty: Opens blocked arteries.

• Open Heart Surgery: Bypass or repair of heart structures.

Electrical Conduction System

• SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers.

EKG and Cardiac Output

• PQRST Wave: Represents electrical activity of the heart.

• Cardiac Output:

Frank-Starling Law

• The greater the stretch of cardiac muscle, the stronger the contraction (up to a limit).

Fetal vs Adult Circulation

• Fetal heart has shunts (foramen ovale, ductus arteriosus) to bypass lungs.

Cardiovascular System: Blood Vessels

Blood Vessel Structure

• Tunica intima: Inner endothelial layer.

• Tunica media: Smooth muscle, controls diameter.

• Tunica externa: Connective tissue, support.

Venipuncture Preference

• Veins are targeted for blood draws due to lower pressure, thinner walls, and accessibility.

Blood Flow Variables

• Blood Pressure (BP): Force exerted by blood on vessel walls.

• Resistance (R): Influenced by vessel length, viscosity, and diameter.

• Blood Flow (BF):

Major Arteries and Veins

• Major arteries branch from the aorta; major veins merge into the superior and inferior vena cava.

Vascular Pathologies

• Aneurysm: Vessel wall bulge; treated by coiling or clipping.

• Stroke: Subarachnoid hemorrhage (bleeding) vs ischemic (blockage).

• Varicose Veins: Dilated, twisted veins; can lead to ulcers.

Lymphatic System

Structure and Function

• Lymphatic vessels, nodes, and valves transport lymph fluid and filter pathogens.

• Lymph fluid forms from interstitial fluid drained from tissues.

Lymphatic Ducts

• Right Lymphatic Duct: Drains right upper body (25%).

• Thoracic Duct: Drains rest of body (75%).

Lymphatic Pathologies

• Lymphedema: Swelling due to lymph blockage (e.g., elephantiasis).

Lymphocytes and Organs

• B and T Lymphocytes: Key immune cells; B cells mature in bone marrow, T cells in thymus.

• Primary Lymphoid Organs: Bone marrow, thymus (site of lymphocyte maturation).

• Secondary Lymphoid Organs: Lymph nodes, spleen, MALT (site of immune response).

Histology

• Lymph node: cortex (B cells), medulla (macrophages).

• Spleen: white pulp (lymphocytes), red pulp (RBCs).

• Peyer's patches: aggregated lymphoid nodules in intestine.

Thymus

• Site of T-lymphocyte maturation.

Immunity System

Innate vs Adaptive Defenses

• Innate: Non-specific, immediate (skin, phagocytes).

• Adaptive: Specific, slower (B and T cells, antibodies).

Humoral Immunity

• Active: Body produces antibodies (natural: infection; artificial: vaccine).

• Passive: Antibodies received (natural: mother to fetus; artificial: injection).

Primary vs Secondary Response

• Secondary response is faster and stronger due to memory cells.

B vs T Lymphocytes

• B cells: Produce antibodies; humoral immunity.

• T cells: Directly attack infected cells; cell-mediated immunity.

Virus Structure and Infection

• Viruses consist of genetic material and protein coat; infect by attachment, entry, replication, assembly, and release.

Vaccines

• Conventional (inactivated/attenuated), mRNA, and viral vector vaccines stimulate immunity.

Immune Cells

• Dendritic Cells: Antigen-presenting cells (APCs).

• CD8 (Cytotoxic) T cells: Kill infected cells.

• CD4 (Helper) T cells: Coordinate immune response.

• Cytokine Storm: Excessive immune response causing tissue damage.

Respiratory System

Anatomy

• Upper Respiratory: Nose, pharynx, larynx.

• Lower Respiratory: Trachea, bronchi, lungs.

• Conducting Zone: Air passageways.

• Respiratory Zone: Gas exchange (alveoli).

Alveoli

• Type I: Squamous cells for gas exchange.

• Type II: Cuboidal cells secrete surfactant.

Pleurae

• Parietal (lines cavity) vs visceral (covers lungs); pleural fluid reduces friction.

Respiratory Physiology

• Pressure Relationships: Atmospheric, intrapulmonary, intrapleural, transpulmonary pressures.

• Boyle's Law: (pressure inversely related to volume).

• Pulmonary Ventilation: Flow =

• Surface Tension & Surfactant: Prevent alveolar collapse.

Respiratory Volumes

• TV (Tidal Volume), IRV (Inspiratory Reserve), ERV (Expiratory Reserve), RV (Residual Volume), FVC (Forced Vital Capacity), TLC (Total Lung Capacity).

• Pulmonary function tests (spirometry):

• Anatomical dead space: Air not involved in gas exchange.

• Minute vs alveolar ventilation rates.

Gas Laws

• Dalton's Law: Total pressure = sum of partial pressures.

• Henry's Law: Gas solubility proportional to partial pressure.

Oxygen-Hemoglobin Dissociation Curve

• Shows hemoglobin saturation at different pO2 levels.

• Shifted by temperature, pH, CO2 (Bohr effect).

CO2 Transport

• Dissolved in plasma (7-10%), bound to hemoglobin (~20%), as bicarbonate (70%).

• Carbonic acid-bicarbonate equation:

Respiratory Pathologies

• Pleurisy, pleural effusion, pneumothorax, atelectasis, hyperventilation, CO poisoning, COPD, decompression sickness ("bends"), lung cancer.

Digestive System

Anatomy

• Alimentary Canal: Mouth to anus (digestive tract).

• Accessory Organs: Teeth, tongue, salivary glands, liver, gallbladder, pancreas.

• Layers: mucosa, submucosa, muscularis externa, serosa.

Digestive Physiology

• Salivary glands (sublingual, submandibular, parotid) secrete amylase and lipase.

• Tooth structure: crown, neck, root; dental diseases include cavities, gingivitis, periodontal disease.

• Swallowing: buccal and pharyngeal-esophageal phases.

• Stomach: fundus, body, pylorus; muscularis externa has three layers.

• Parietal cells secrete HCl and intrinsic factor; chief cells secrete pepsinogen (activated to pepsin by HCl).

• Mucosal barrier protects stomach lining; ulcers often caused by H. pylori.

• HCl secretion involves H+/K+ ATPase pumps and the alkaline tide.

• Carbonic acid-bicarbonate equation:

Liver, Gallbladder, Pancreas

• Liver functions: bile formation, glycogen storage, detoxification, protein production, ammonia to urea conversion, angiotensinogen production, albumin synthesis, cholesterol production.

• Gallbladder stores bile; cystic and hepatic ducts form the common bile duct.

• Pancreas secretes proteases, amylase, lipases, nucleases.

Small and Large Intestine

• Small intestine: microvilli increase absorption; lacteals absorb fats.

• Large intestine: absorbs water, produces vitamin K, houses bacteria.

Digestive Hormones

Digestive Pathologies

• Metabolic acidosis, H. pylori infection, GERD, Barrett's esophagus, hepatitis, NAFLD, cirrhosis, gallstones, cholangiocarcinoma, pancreatic cancer, constipation, diverticulosis/diverticulitis, colorectal cancer.

Urinary System

Renal Anatomy

• Kidney structure: cortex, medulla, pelvis.

• Blood flow: renal artery → segmental → interlobar → arcuate → cortical radiate → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta → veins.

• Nephron: Bowman's capsule, PCT, loop of Henle, DCT, collecting duct.

• Juxtaglomerular complex: macula densa (NaCl sensors), granular cells (BP sensors, secrete renin).

Renal Physiology

• Glomerular filtration: filtration membrane, GFR depends on net filtration pressure, surface area, permeability.

• Tubular reabsorption: primary/secondary active transport, diffusion, osmosis; transport maximum (e.g., glucose in diabetes).

• ADH targets aquaporins in collecting ducts; aldosterone targets Na+/K+ pumps in DCT and collecting ducts.

Urinalysis

• Normal urine: water, urea, uric acid, creatinine, ions, urochrome; pH ~6.0; specific gravity 1.001–1.0035.

Urinary Pathologies

• Abnormal constituents (protein, glucose, blood, etc.), renal failure (BUN test), glomerulonephritis, chronic renal disease (GFR < 60 ml/min for 3+ months), renal failure (GFR < 15 ml/min), nephrotic syndrome, eGFR disparities.

• Treatments: peritoneal dialysis, hemodialysis.

Renal Homeostasis

• Carbonic acid-bicarbonate equation:

• RAAS (Renin-Angiotensin-Aldosterone System): regulates BP and fluid balance.

Reproductive System

Male Anatomy

• Testis (seminiferous tubules, rete testis, interstitial cells), epididymis, spermatic cord, ductus deferens, ampulla, seminal gland, ejaculatory duct, prostatic urethra, prostate gland, bulbo-urethral gland, penile urethra, penis (corpus cavernosum/spongiosum), glans, prepuce, external orifice.

• Sperm structure and blood-testis barrier.

Male Pathology

• Benign prostate hypertrophy, prostate cancer (PSA, DRE), erectile dysfunction.

Female Anatomy

• Ovaries, uterine tubes, uterus, cervix, vagina, external genitalia, mammary glands.

• Uterine (menstrual) cycle: ovarian and uterine phases.

• Menopause and hormone replacement therapy (HRT).

Female Pathology

• Breast/ovarian cancer, HPV/cervical cancer, STIs (chlamydia, gonorrhea, syphilis), polycystic ovarian syndrome, pelvic inflammatory disease, endometriosis, ectopic pregnancy.

Additional info: Where figures or tables are referenced but not provided, standard textbook content has been summarized. For equations, the carbonic acid-bicarbonate buffer system is central to acid-base balance in blood, respiratory, and urinary systems. The RAAS system is crucial for blood pressure regulation.