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

Homeostasis and Feedback Mechanisms

Definition of Homeostasis

Homeostasis is the process by which the body maintains a stable internal environment despite changes in external conditions. This dynamic equilibrium is essential for the survival and proper functioning of organisms.

• 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 amplifies the original stimulus. Example: Blood clotting, labor contractions during childbirth.

Systems Involved in Feedback

• Nervous System: Provides rapid, short-term, and targeted responses (e.g., muscle contraction, gland secretion).

• Endocrine System: Provides slower, long-lasting, and widespread effects via hormones.

Endocrine System

Endocrine vs. Exocrine Glands

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

• Exocrine Glands: Secrete products into ducts that lead to body surfaces or cavities (e.g., sweat, salivary glands).

Hormones and Receptors

• Hormone: A chemical messenger secreted by endocrine glands, transported by blood, and acting on distant target cells.

• Hormonal Receptors:

  • Cell Surface Receptors: Bind amino acid-based (peptide) hormones; trigger second messenger systems.

  • Intracellular Receptors: Bind steroid hormones; directly influence gene expression.

Insulin & Glucagon

• Secreted by: Pancreatic islets (Islets of Langerhans)

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

• Glucagon: Released in response to low blood glucose; raises blood glucose 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

• Ingestion

• Propulsion (including peristalsis)

• Mechanical breakdown (including mastication)

• Digestion (chemical breakdown)

• Absorption (mainly in the small intestine)

• Defecation

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.

Layers of the GI Tract

• Mucosa: Innermost layer; secretion and absorption.

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

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

• Serosa: Outermost layer; protective.

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: Synthesis of complex molecules from simpler ones; requires energy.

• Catabolism: Breakdown of 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 Production:

  • Glycolysis: $2$ ATP per glucose molecule

  • Glycolysis + Krebs Cycle + Electron Transport Chain: $\approx 30-32$ ATP per glucose molecule

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

• Carbon Dioxide: Produced during the Krebs cycle as a waste product of metabolism.

Nutrient Absorption States

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

• Post-Absorptive State: GI tract is empty; energy needs are met by breaking down reserves (catabolism).

Respiratory System

Major Function

The respiratory system supplies the body with oxygen and removes carbon dioxide through the process of respiration.

Four Processes of Respiration

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

• External Respiration: Gas exchange between lungs and blood.

• Transport of Gases: Movement of oxygen and carbon dioxide in the blood.

• 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; low in tissues and venous blood.

Carbon Dioxide Transport

• Transported: Dissolved in plasma, bound to hemoglobin, and as bicarbonate ions ($\mathrm{HCO_3^-}$).

• Partial Pressure: High in tissues and venous blood; 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, and waste products.

• Formed Elements:

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

  • Leukocytes (WBCs): Defend against infection.

  • 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 deoxygenated blood from the right side of the heart to the lungs and returns oxygenated blood to the left side.

• Systemic Circuit: Carries oxygenated blood from the left side of the heart to the body and returns deoxygenated blood to the right side.

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 lymphatic 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

• Branches:

  • 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: Essential 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 and electrolyte balance

• Regulate blood pressure and pH

Structure of Nephrons

• Renal Corpuscle:

  • Glomerulus: Capillary network for filtration

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

• Renal Tubule:

  • Proximal convoluted tubule

  • Nephron loop (Loop of Henle)

  • Distal convoluted tubule

Filtrate vs. Urine

• Filtrate: Fluid filtered from blood in the glomerulus; contains water, ions, glucose, amino acids, and wastes

• 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