Comprehensive Study Notes for Human Anatomy & Physiology: Homeostasis, Endocrine, Digestive, Metabolism, Respiratory, Blood, Cardiovascular, Lymphatic/Immune, and Urinary Systems

Homeostasis and Feedback Mechanisms

Definition and Importance of Homeostasis

Homeostasis refers to the body's ability to maintain a stable internal environment despite changes in external conditions. This dynamic equilibrium is essential for normal physiological function and survival.

• Homeostatic Imbalance: A disturbance in homeostasis, which can lead to disease or dysfunction.

Feedback Mechanisms

• Negative Feedback: The most common mechanism; it reduces or shuts off the original stimulus. Example: Regulation of body temperature, blood glucose by insulin.

• Positive Feedback: Enhances or exaggerates the original stimulus. Example: Blood clotting, labor contractions during childbirth.

Systems Involved in Feedback

• Nervous System: Fast, brief responses; targets specific cells (muscle fibers or glands).

• Endocrine System: Slower, longer-lasting responses; targets cells throughout the body via hormones.

Endocrine System

Endocrine vs. Exocrine Glands

• Endocrine Glands: Ductless; secrete hormones directly into the bloodstream (e.g., pituitary, thyroid).

• Exocrine Glands: Have ducts; secrete substances onto epithelial surfaces (e.g., sweat, salivary glands).

Hormones and Receptors

• Hormone: A chemical messenger secreted by endocrine glands, traveling through the blood to target organs.

• Hormonal Receptors:

  • Cell Surface Receptors: Bind amino acid-based hormones (e.g., insulin).

  • Intracellular Receptors: Bind steroid hormones (e.g., cortisol) that can cross the cell membrane.

Insulin & Glucagon

• Secreted by: Pancreatic islets (Islets of Langerhans)

• Insulin: Released in response to high blood glucose; lowers blood sugar by promoting cellular uptake.

• Glucagon: Released in response to low blood glucose; raises blood sugar by stimulating glycogen breakdown.

Types of Diabetes

• Type 1 Diabetes: Autoimmune destruction of insulin-producing cells; requires insulin therapy.

• Type 2 Diabetes: Insulin resistance; often associated with obesity and lifestyle factors.

Digestive System

General Functions and Divisions

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It consists of the alimentary canal (GI tract) and accessory organs (liver, pancreas, gallbladder).

Six Essential Activities of Digestion

1. Ingestion

2. Propulsion (including swallowing and peristalsis)

3. Mechanical Breakdown (chewing, churning)

4. Digestion (enzymatic breakdown)

5. Absorption (nutrients enter blood/lymph)

6. Defecation (elimination of indigestible substances)

Peritoneum and Related Terms

• Peritoneum: Serous membrane lining the abdominal cavity and covering abdominal organs.

• Visceral Peritoneum: Covers organs.

• Parietal Peritoneum: Lines the cavity wall.

• Mesentery: Double layer of peritoneum that supports organs.

Layers of the GI Tract

• Mucosa: Innermost; secretes mucus, absorbs nutrients, protects.

• Submucosa: Connective tissue with blood vessels, nerves, glands.

• Muscularis Externa: Smooth muscle; responsible for peristalsis and segmentation.

• Serosa: Outermost; protective layer.

Key Terms

• Peristalsis: Wave-like muscle contractions moving food along the GI tract.

• Mastication: Chewing.

• Deglutition: Swallowing.

• Most nutrient absorption occurs in: The small intestine.

Metabolism

Anabolism and Catabolism

• Anabolism: Building up complex molecules from simpler ones (requires energy).

• Catabolism: Breaking down complex molecules into simpler ones (releases energy).

Enzymes

• Definition: Biological catalysts that speed up chemical reactions without being consumed.

• Importance: Lower activation energy, allowing metabolic reactions to occur rapidly at body temperature.

Adenosine Triphosphate (ATP)

• ATP: The primary energy currency of the cell.

• ATP from Glycolysis: 2 ATP per glucose molecule.

• ATP from Glycolysis, Krebs Cycle, and Electron Transport: Up to 32 ATP per glucose molecule.

• Oxygen: Required as the final electron acceptor in the electron transport chain.

• CO2: Produced during the Krebs cycle as a waste product of cellular respiration.

Nutrient Absorption States

• Absorptive State: Nutrients are being absorbed; anabolism exceeds catabolism.

• Post-Absorptive State: GI tract is empty; body relies on stored nutrients; catabolism exceeds anabolism.

Respiratory System

Major Function

The respiratory system supplies the body with oxygen and removes carbon dioxide through gas exchange.

Four Processes of Respiration

1. Pulmonary Ventilation: Movement of air into and out of the lungs.

2. External Respiration: Gas exchange between lungs and blood.

3. Transport of Gases: Movement of O2 and CO2 in the blood.

4. Internal Respiration: Gas exchange between blood and tissues.

Oxygen Transport

• Transported: Mostly bound to hemoglobin in red blood cells; a small amount dissolved in plasma.

• Partial Pressure High: In alveoli and arterial blood.

• Partial Pressure Low: In tissues and venous blood.

Carbon Dioxide Transport

• Transported: As bicarbonate ions (majority), bound to hemoglobin, and dissolved in plasma.

• Partial Pressure High: In tissues and venous blood.

• Partial Pressure Low: In alveoli and arterial blood.

Blood

General Functions

• Transport of gases, nutrients, wastes, and hormones.

• Regulation of pH, temperature, and fluid volume.

• Protection against infection and blood loss.

Components of Blood

• Plasma: Liquid matrix (~55% of blood); contains water, proteins, nutrients, hormones, wastes.

• Formed Elements:

  • Erythrocytes (RBCs): Transport oxygen and carbon dioxide.

  • Leukocytes (WBCs): Defend against pathogens.

  • Platelets: Involved in blood clotting.

Blood Grouping

• Agglutinogens: Antigens on the surface of RBCs (determine blood type).

• Agglutinins: Antibodies in plasma that react with agglutinogens.

• Types: A, B, AB, O (based on presence/absence of A and B agglutinogens).

Blood Type	Agglutinogens (Antigens)	Agglutinins (Antibodies)
A	A	Anti-B
B	B	Anti-A
AB	A and B	None
O	None	Anti-A and Anti-B

Heart and Blood Vessels

Pulmonary and Systemic Circuits

• Pulmonary Circuit: Carries blood from the heart to the lungs and back (right side of heart).

• Systemic Circuit: Carries blood from the heart to the rest of the body and back (left side of heart).

General Structure of the Heart

• Coverings: Pericardium (fibrous and serous layers).

• Chambers: 2 atria (upper), 2 ventricles (lower).

• Valves: Atrioventricular (tricuspid, bicuspid/mitral) and semilunar (pulmonary, aortic).

Pathway of Blood Through the Heart

1. Right atrium → right ventricle → pulmonary arteries → lungs

2. Lungs → pulmonary veins → left atrium → left ventricle → aorta → body

Phases of the Cardiac Cycle

• Systole: Contraction phase; blood is pumped out.

• Diastole: Relaxation phase; chambers fill with blood.

Arteries vs. Veins

• Arteries: Carry blood away from the heart; thicker walls, higher pressure.

• Veins: Carry blood toward the heart; thinner walls, valves to prevent backflow.

Pulse and Blood Pressure

• Pulse: Rhythmic expansion of arteries due to heartbeat.

• Blood Pressure: Force of blood against vessel walls; measured as systolic/diastolic (e.g., 120/80 mmHg).

Lymphatic and Immune System

General Functions

• Returns excess tissue fluid to the bloodstream.

• Absorbs dietary fats.

• Defends against pathogens.

Main Parts of the Lymphatic System

• Lymphatics: Network of vessels.

• Lymph: Fluid transported by lymphatics.

• Lymph Nodes: Filter lymph and house immune cells.

Innate Defenses

• First Line: Skin and mucous membranes (physical and chemical barriers).

• Second Line: Phagocytes, natural killer cells, inflammation, antimicrobial proteins, fever.

Adaptive Defenses

• Characteristics: Specificity, memory, systemic response.

• Humoral Immunity: B-cells produce antibodies targeting extracellular pathogens.

• Cellular Immunity: T-cells target infected or abnormal cells directly or indirectly.

• Importance of T-cells: Critical for cell-mediated immunity and regulation of immune responses.

• Antigen: Any substance that can provoke an immune response.

Urinary System

General Components

• Kidneys, ureters, urinary bladder, urethra.

Functions of the Kidneys

• Filter blood to remove wastes.

• Regulate fluid, electrolyte, and acid-base balance.

• Produce hormones (e.g., erythropoietin, renin).

Structure of Nephrons

• Nephron: Functional unit of the kidney.

• Renal Corpuscle:

  • Glomerulus: Capillary network for filtration.

  • Glomerular Capsule (Bowman's capsule): Surrounds glomerulus; collects filtrate.

• Renal Tubule:

  • Proximal Convoluted Tubule (PCT): Reabsorption of water, ions, nutrients.

  • Nephron Loop (Loop of Henle): Concentrates urine.

  • Distal Convoluted Tubule (DCT): Further reabsorption and secretion.

Filtrate vs. Urine

• Filtrate: Fluid filtered from blood at the glomerulus; contains water, ions, small molecules.

• Urine: Final product after reabsorption and secretion; contains wastes and excess substances.

Three Steps of Urine Formation

1. Glomerular Filtration

2. Tubular Reabsorption

3. Tubular Secretion