Anatomy & Physiology Study Notes: Endocrine System, Blood, Heart, and Blood Vessels

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Chapter 16: The Endocrine System

Autocrines, Paracrines, and Hormones

The body uses chemical messengers to regulate physiological processes. These messengers differ in their targets and mechanisms:

Autocrines: Chemicals that exert effects on the same cells that secrete them.
Paracrines: Chemicals that act locally (within the same tissue) but affect cells other than those that secrete them.
Hormones: Long-distance chemical signals that travel in blood or lymph throughout the body to regulate the activity of target cells.

Endocrine vs. Exocrine Glands

Endocrine glands: Ductless glands that secrete hormones directly into the bloodstream (e.g., pituitary, thyroid).
Exocrine glands: Glands that release their secretions onto epithelial surfaces via ducts (e.g., sweat, salivary glands).

Classification of Hormones

Amino acid-based hormones: Includes most hormones; water-soluble and act on plasma membrane receptors.
Steroid hormones: Synthesized from cholesterol; lipid-soluble and act on intracellular receptors (e.g., gonadal and adrenocortical hormones).

Hormone Action and Target Cell Activation

A target cell must have specific receptors for a hormone to respond.
Hormone effects depend on blood levels, number of receptors, and receptor affinity.

Regulation of Hormone Release

Humoral stimuli: Changes in blood levels of ions/nutrients (e.g., Ca2+ stimulates parathyroid hormone release).
Neural stimuli: Nerve fibers stimulate hormone release (e.g., sympathetic stimulation of adrenal medulla to release epinephrine).
Hormonal stimuli: Hormones stimulate other endocrine glands to release hormones (e.g., hypothalamic hormones stimulate anterior pituitary).

Mechanisms of Hormone Interaction

Permissiveness: One hormone cannot exert its effects without another hormone present (e.g., reproductive hormones need thyroid hormone).
Synergism: More than one hormone produces the same effects, amplifying the result (e.g., glucagon and epinephrine increase blood glucose).
Antagonism: One hormone opposes the action of another (e.g., insulin vs. glucagon).

Pituitary Gland: Anterior vs. Posterior

Anterior pituitary (adenohypophysis): Glandular tissue; synthesizes and releases hormones.
Posterior pituitary (neurohypophysis): Neural tissue; stores and releases hormones made by the hypothalamus.

Hormones of the Pituitary Gland

Posterior pituitary: Oxytocin, Antidiuretic hormone (ADH)
Anterior pituitary: Growth hormone (GH), Thyroid-stimulating hormone (TSH), Adrenocorticotropic hormone (ACTH), Follicle-stimulating hormone (FSH), Luteinizing hormone (LH), Prolactin (PRL)

Disorders of Hormone Secretion

Hyposecretion: Too little hormone (e.g., diabetes insipidus, pituitary dwarfism)
Hypersecretion: Too much hormone (e.g., gigantism, acromegaly)

Thyroid and Parathyroid Glands

Thyroid follicles: Spherical structures with follicular cells producing thyroglobulin; colloid in lumen stores thyroglobulin and iodine for thyroid hormone synthesis.
T3 (triiodothyronine): More active form; T4 (thyroxine): Major form secreted, converted to T3 in tissues.
Calcitonin: Lowers blood calcium levels; secreted by parafollicular cells.
Parathyroid hormone (PTH): Increases blood calcium levels; antagonist to calcitonin.

Adrenal Glands

Adrenal cortex:
- Zona glomerulosa: Mineralocorticoids (e.g., aldosterone)
- Zona fasciculata: Glucocorticoids (e.g., cortisol)
- Zona reticularis: Gonadocorticoids (e.g., androgens)
Adrenal medulla: Catecholamines (epinephrine, norepinephrine)

Other Endocrine Organs and Hormones

Pineal gland: Secretes melatonin, regulates sleep-wake cycles, antioxidant effects.
Pancreas:
- Insulin (from beta cells): Lowers blood glucose, promotes storage.
- Glucagon (from alpha cells): Raises blood glucose, promotes breakdown of glycogen.
Diabetes mellitus: Chronic high blood glucose due to insulin deficiency or resistance.

Chapter 17: Blood

Composition and Characteristics of Blood

Hematocrit: Percentage of blood volume occupied by erythrocytes (RBCs). Normal: Males 47% ± 5%, Females 42% ± 5%.
Other components: Plasma (~55%), leukocytes and platelets (<1%).
Blood is sticky, opaque, with a metallic taste; slightly alkaline (pH 7.35–7.45).

Functions of Blood

Distribution: Transports oxygen, nutrients, hormones, and waste products.
Regulation: Maintains body temperature, pH, and fluid volume.
Protection: Prevents blood loss (clotting) and infection (immune cells).

Plasma and Formed Elements

Plasma: 90% water; contains electrolytes, plasma proteins (albumin, globulins, fibrinogen), nutrients, gases, hormones, and waste products.
Formed elements: Erythrocytes (RBCs), leukocytes (WBCs), platelets. Most do not divide; replaced by stem cells in bone marrow.

Erythrocytes (Red Blood Cells)

Biconcave discs, 7.5 μm diameter, anucleate, filled with hemoglobin for gas transport.
Flexible to pass through capillaries.
Hemoglobin: Four globin chains, each with a heme group (iron atom binds O2).
Types: Oxyhemoglobin (O2-bound), deoxyhemoglobin (O2-released), carbaminohemoglobin (CO2-bound).
Erythropoiesis: Production of RBCs, stimulated by erythropoietin (EPO) from kidneys.
RBCs broken down by macrophages; iron recycled, heme degraded to bilirubin, globin to amino acids.

Leukocytes (White Blood Cells)

Major function: Immunity and defense against pathogens.
Granulocytes: Neutrophils, eosinophils, basophils (contain granules).
Agranulocytes: Lymphocytes, monocytes (lack visible granules).
Percentages: Neutrophils (~60–70%), lymphocytes (~20–25%), monocytes (~3–8%), eosinophils (~2–4%), basophils (~0.5–1%).
Lymphocyte formation differs as they mature in lymphoid tissues.

Platelets and Hemostasis

Megakaryocytes: Large bone marrow cells that fragment to form platelets.
Platelets: Essential for blood clotting (hemostasis).
Three steps of hemostasis:
1. Vascular spasm: Vessel constricts to reduce blood flow.
2. Platelet plug formation: Platelets adhere to exposed collagen and aggregate.
3. Coagulation: Fibrin mesh forms, stabilizing the clot (involves clotting factors).
Clot retraction: Platelets contract to shrink the clot.
Fibrinolysis: Clot is dissolved by plasmin.
Clot formation limited by inactivation of unbound thrombin, prostacyclin, heparin, smooth endothelium, and blood flow.

Blood Disorders

Thrombi: Clots in unbroken vessels.
Emboli: Free-floating clots.
Hemophilia: Genetic deficiency of clotting factors.
Leukemia: Cancer of WBCs.
Leukocytosis: Elevated WBC count.

Chapter 18: The Heart and Cardiovascular System

Pulmonary vs. Systemic Circuits

Pulmonary circuit: Right side of heart pumps blood to lungs (low O2 to high O2).
Systemic circuit: Left side pumps oxygenated blood to body tissues.
Vessels: Arteries carry blood away from heart; veins return blood to heart.

Heart Anatomy

Pericardium: Double-walled sac; fibrous pericardium (outer), serous pericardium (parietal and visceral layers).
Heart wall: Epicardium (outer), myocardium (muscle), endocardium (inner lining).
Cardiac skeleton: Dense connective tissue supporting valves and muscle attachment.
Chambers: Two atria (receiving), two ventricles (pumping).
Valves: Atrioventricular (tricuspid, mitral), semilunar (pulmonary, aortic).
Valves open/close due to pressure differences.

Coronary Circulation

Coronary arteries: Supply oxygenated blood to heart muscle (e.g., left and right coronary arteries, circumflex, anterior interventricular).
Cardiac veins: Drain deoxygenated blood from myocardium into coronary sinus.

Blood Flow Through the Heart

Right atrium → right ventricle → pulmonary trunk → lungs → left atrium → left ventricle → aorta → body.

Cardiac Muscle vs. Skeletal Muscle

Cardiac muscle: Branched, striated, intercalated discs, involuntary, single nucleus.
Skeletal muscle: Long, cylindrical, multinucleate, voluntary.
Intercalated discs: Contain gap junctions (electrical coupling) and desmosomes (mechanical strength).

Intrinsic Conduction System

Pacemaker cells generate action potentials.
Pathway: SA node → AV node (delays impulse) → AV bundle → bundle branches → Purkinje fibers.

Cardiac Cycle and Output

ECG waves: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).
Cardiac cycle: All events in one heartbeat (systole and diastole).
Cardiac output (CO): Volume of blood pumped per minute.
- Formula:
- Where = heart rate, = stroke volume.
Stroke volume regulated by preload, contractility, afterload.
Heart rate regulated by autonomic nervous system, hormones, ions.
Tachycardia: Abnormally fast heart rate.
Bradycardia: Abnormally slow heart rate.

Chapter 19: The Blood Vessels

Structure of Blood Vessels

Three tunics (layers):
- Tunica intima: Endothelium (simple squamous epithelium).
- Tunica media: Smooth muscle and elastic fibers.
- Tunica externa: Collagen fibers; contains vasa vasorum (small vessels that supply large vessel walls).

Types of Arteries and Capillaries

Elastic arteries: Large, near heart, conduct blood, withstand pressure fluctuations.
Muscular arteries: Distribute blood to organs, more smooth muscle.
Arterioles: Smallest arteries, control blood flow into capillaries.
Capillaries: Smallest vessels; types:
- Continuous: Least permeable, most common (e.g., skin, muscle).
- Fenestrated: Pores for increased permeability (e.g., kidneys, intestines).
- Sinusoidal: Most permeable, large gaps (e.g., liver, bone marrow).
Capillaries are just large enough for RBCs to pass through single file.

Microcirculation and Venous Return

Microcirculation: Arterioles → capillaries → venules.
Precapillary sphincters regulate blood flow into capillary beds.
Venules collect blood from capillaries; WBCs can leave bloodstream here.
Venous adaptations: Valves, muscle pump, respiratory pump help return blood to heart.

Blood Flow, Pressure, and Resistance

Blood flow (F): Volume of blood flowing through a vessel, organ, or circulation per unit time.
Blood pressure (P): Force per unit area exerted on vessel wall by blood.
Resistance (R): Opposition to flow; mainly from vessel diameter, length, and blood viscosity.
Relationship:
Laminar flow: Smooth, streamlined; turbulent flow: Irregular, increases resistance.

Types of Blood Pressure

Systolic: Peak pressure during ventricular contraction.
Diastolic: Lowest pressure during ventricular relaxation.
Pulse pressure: Difference between systolic and diastolic.
Mean arterial pressure (MAP): Average pressure in arteries.
- Formula:
Largest pressure drop occurs in arterioles; veins have lowest pressure due to distance from heart and larger lumen.

Blood Pressure Regulation

Short-term (neural): Cardiovascular center in medulla, baroreceptors, chemoreceptors, hypothalamus, hormones.
Long-term (renal): Renin-angiotensin-aldosterone system regulates blood volume and pressure.

Blood Pressure Disorders

Hypertension: High blood pressure; primary (no cause), secondary (identifiable cause).
Hypotension: Low blood pressure; orthostatic (upon standing), not always pathological.

Capillary Exchange

Hydrostatic pressure: Pushes fluid out of capillaries (higher at arteriole end).
Colloid osmotic pressure: Pulls fluid into capillaries (higher at venous end).
Four routes for molecules: Diffusion through membrane, intercellular clefts, fenestrations, vesicular transport.

Vessel Type	Main Features	Function
Elastic artery	Thick wall, large lumen, elastic tissue	Conduct blood, dampen pressure
Muscular artery	More smooth muscle, less elastic	Distribute blood to organs
Arteriole	Smallest artery, thin wall	Control flow into capillaries
Capillary	Single endothelial layer	Exchange of gases, nutrients
Venule	Smallest vein	Collect blood from capillaries
Vein	Thin wall, large lumen, valves	Return blood to heart

Additional info: These notes expand on the study guide by providing definitions, mechanisms, and examples for each topic, as well as formulas and a summary table for vessel types. For comprehensive exam preparation, refer to class PowerPoints and assigned readings.