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

Endocrine System

Mechanisms of Cellular Communication

The endocrine system communicates via chemical messengers called hormones, which regulate physiological activities throughout the body. It is distinct from the nervous system, which uses electrical impulses for rapid communication.

• Nervous vs. Endocrine System: The nervous system provides fast, short-term responses, while the endocrine system offers slower, long-lasting effects.

• Cell Activity Control: Hormones influence cell activity by binding to specific receptors, triggering cellular responses.

Hormones

Hormones are classified based on their solubility and mechanisms of action.

• Classes Based on Solubility:

  • Lipid-soluble hormones: (e.g., steroid hormones) pass through cell membranes and bind to intracellular receptors.

  • Water-soluble hormones: (e.g., peptide hormones) bind to membrane receptors and use second messenger systems.

• Direct Gene Activation: Lipid-soluble hormones directly affect gene expression by binding to DNA.

• Second Messenger Systems: Water-soluble hormones activate intracellular signaling cascades (e.g., cAMP).

• Stimulation Methods: Neural, hormonal, and humoral stimuli can trigger hormone release.

Endocrine Organs and Hormones

Major endocrine organs produce specific hormones that regulate body functions.

• Hypothalamus: Produces releasing and inhibiting hormones, controls pituitary gland.

  • Hormones: Oxytocin, Antidiuretic Hormone (ADH)

• Pituitary Gland: Divided into anterior (adenohypophysis) and posterior (neurohypophysis) lobes.

  • Anterior Pituitary Hormones: TSH, ACTH, FSH, LH, GH, PRL, MSH

  • Posterior Pituitary Hormones: Oxytocin, ADH

• Thyroid Gland: Produces hormones regulating metabolism.

  • Thyroxine (T4), Triiodothyronine (T3), Calcitonin

• Parathyroid Glands: Secrete parathyroid hormone (PTH) to regulate calcium levels.

• Adrenal Glands: Consist of cortex and medulla.

  • Cortex: Produces corticosteroids (e.g., cortisol, aldosterone)

  • Medulla: Produces catecholamines (e.g., epinephrine, norepinephrine)

• Pancreas: Contains islets of Langerhans.

  • Alpha cells: Secrete glucagon

  • Beta cells: Secrete insulin

• Gonads: Ovaries and testes produce sex hormones.

  • Testes: Testosterone

  • Ovaries: Estrogen, Progesterone

Hormone Interactions & General Adaptation Syndrome (GAS)

Hormones can interact synergistically, antagonistically, or permissively. The General Adaptation Syndrome describes the body's response to stress in three stages: alarm, resistance, and exhaustion.

• Synergistic: Hormones amplify each other's effects.

• Antagonistic: Hormones oppose each other's effects.

• Permissive: One hormone enables another to act.

• GAS Stages: Alarm (fight or flight), Resistance (adaptation), Exhaustion (depletion of resources).

Blood

Functions and Components of Blood

Blood is a connective tissue with multiple functions, including transport, regulation, and protection.

• Functions: Transport gases, nutrients, hormones; regulate pH and temperature; protect against pathogens.

• Components:

  • Plasma: Water, electrolytes, proteins

  • Formed Elements: Red blood cells (RBCs), white blood cells (WBCs), platelets

Electrolytes in Blood

Electrolytes help maintain osmotic balance and are essential for cellular function.

• Common Electrolytes: Sodium, potassium, calcium, chloride

Erythrocytes (RBCs)

Red blood cells are specialized for oxygen transport.

• Shape: Biconcave disc increases surface area for gas exchange.

• Hemoglobin: Protein that binds oxygen; contains iron (Fe).

• Erythropoietin (EPO): Hormone that stimulates RBC production.

Hematopoiesis

Hematopoiesis is the process of blood cell formation, occurring primarily in the bone marrow.

• Blood Cell Lineages:

  • RBCs: Erythroblast → Reticulocyte → Erythrocyte

  • WBCs: Lymphoid vs. myeloid stem cells; lymphocytes, granulocytes, monocytes

  • Platelets: Derived from megakaryocytes

• Hemoglobin Breakdown: Heme → Biliverdin → Bilirubin

Blood Typing

Blood typing is based on the presence of antigens on RBCs and corresponding antibodies in plasma.

• ABO System: Types A, B, AB, O

• Rh Factor: Positive or negative

• Transfusions: Compatibility is crucial to prevent reactions.

Leukocytes (WBCs)

White blood cells are key to immune defense.

• Granular vs. Agranular: Granulocytes (neutrophils, eosinophils, basophils); Agranulocytes (lymphocytes, monocytes)

• Functions: Phagocytosis, antibody production, immune regulation

• Differential WBC Count: Used to diagnose infections and diseases

Hemostasis

Hemostasis is the process of stopping bleeding, involving vascular spasm, platelet plug formation, and coagulation.

• Steps: Vasoconstriction, platelet aggregation, fibrin clot formation

Heart

Location & Orientation

The heart is located in the mediastinum of the thoracic cavity, oriented with its base at the top and apex pointing left.

• External Anatomy: Base, apex, right and left atrium, right and left ventricles, coronary sulcus, interventricular sulcus, pericardium

Internal Anatomy

The heart contains four chambers and four main valves that regulate blood flow.

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

• Valves:

  • Right AV (tricuspid), Left AV (bicuspid/mitral)

  • Pulmonary semilunar, aortic semilunar

• Additional Structures: Chordae tendineae, papillary muscles, trabeculae carneae

Coronary Circulation

Coronary arteries supply the heart muscle with oxygenated blood.

• Major Arteries: Left and right coronary arteries, marginal, circumflex, anterior and posterior descending arteries

• Veins: Great cardiac vein, coronary sinus

Pulmonary & Systemic Circuits

The heart pumps blood through two circuits: pulmonary (to lungs) and systemic (to body).

• Trace of Blood Flow: Vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body

Cardiac Cycle

The cardiac cycle consists of systole (contraction) and diastole (relaxation).

• Heart Sounds: S1 (AV valves close), S2 (semilunar valves close)

Cardiac Muscle Tissue

Cardiac muscle cells are striated, branched, and interconnected by intercalated discs for synchronized contraction.

Electrocardiogram (ECG)

An ECG records the electrical activity of the heart, showing waves and intervals that correspond to different phases of the cardiac cycle.

• Waves: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization)

Autonomic Heart Rate Effects

The autonomic nervous system regulates heart rate via sympathetic and parasympathetic pathways.

• Bradycardia: Slow heart rate

• Tachycardia: Fast heart rate

• Cardioinhibitory Center: Parasympathetic control

• Cardioacceleratory Center: Sympathetic control

Stroke Volume

Stroke volume is the amount of blood ejected by the left ventricle per beat.

• Preload: Degree of stretch of cardiac muscle before contraction

• Afterload: Pressure the heart must overcome to eject blood

• Isovolumetric Contraction/Relaxation: Phases where ventricles contract/relax without volume change

Formula:

$\text{Stroke Volume (SV)} = \text{End Diastolic Volume (EDV)} - \text{End Systolic Volume (ESV)}$

Blood Vessels

Structure of Blood Vessels

Blood vessels are composed of three layers: tunica intima, tunica media, and tunica externa.

• Types: Arteries, veins, capillaries

• Cell Types: Endothelial cells, smooth muscle cells

Capillary Types & Pathways

Capillaries are classified by permeability and structure.

• Types: Continuous, fenestrated, sinusoidal

• Pathways: Collaterals, anastomoses, sphincters

Venous Valves

Valves in veins prevent backflow and aid venous return to the heart.

Blood Flow Influences

Blood flow is affected by vessel length, diameter, viscosity, and turbulence.

• Vascular Resistance: Increases with length and decreases with diameter

• Viscosity: Thickness of blood

• Turbulence: Disordered flow, increases resistance

Blood Pressure

Blood pressure is the force exerted by blood on vessel walls.

• Systolic Pressure: During ventricular contraction

• Diastolic Pressure: During ventricular relaxation

• Hypertension: Chronically elevated blood pressure

Formula:

$\text{Blood Pressure (BP)} = \text{Cardiac Output (CO)} \times \text{Total Peripheral Resistance (TPR)}$

Capillary Exchange

Capillary exchange involves filtration and reabsorption, driven by hydrostatic and osmotic pressures.

• Pressures: Blood hydrostatic pressure (BHP), blood colloid osmotic pressure (BCOP), net filtration pressure (NFP)

Regulation of Blood Flow

Blood flow is regulated by local (autoregulation), neural, and hormonal mechanisms.

• Autoregulation: Local control via precapillary sphincters

• Central Regulation: Baroreceptors (pressure), chemoreceptors (chemical)

• Endocrine Response: Hormones adjust blood pressure and volume

Exercise Adjustments & Arteriosclerosis

Exercise increases cardiac output and redistributes blood flow. Arteriosclerosis is the hardening of arteries, reducing elasticity and increasing blood pressure.

Blood Vessel Type	Main Function	Structural Features
Artery	Carry blood away from heart	Thick tunica media, high pressure
Vein	Carry blood toward heart	Thin walls, valves present
Capillary	Exchange of gases/nutrients	Single endothelial layer

Additional info: Some details, such as the full list of hormones and blood cell lineages, were expanded for academic completeness.