Endocrine System

Endocrine Glands and Their Functions

The endocrine system consists of glands that secrete hormones directly into the bloodstream to regulate various body functions. These glands play a crucial role in maintaining homeostasis, growth, metabolism, and reproduction.

• Endocrine Glands: Include the pituitary, thyroid, parathyroid, adrenal, pineal, and gonads (ovaries and testes).

• Hormones: Chemical messengers that influence target cells and organs.

• Major Processes Controlled: Growth, metabolism, stress response, reproduction, and electrolyte balance.

• Examples: Insulin (regulates blood glucose), thyroid hormones (regulate metabolism), cortisol (stress response).

Key Endocrine Glands and Hormones

• Hypothalamus: Located in the brain; controls the pituitary gland and links the nervous and endocrine systems. Produces releasing and inhibiting hormones.

• Pituitary Gland: "Master gland" located at the base of the brain. Divided into anterior and posterior lobes. Secretes hormones such as ACTH, FSH, LH, GH, PRL, TSH, ADH, and oxytocin.

• Thyroid Gland: Located in the neck; produces thyroxine (T4) and triiodothyronine (T3) to regulate metabolism.

• Parathyroid Glands: Four small glands on the posterior thyroid; secrete parathyroid hormone (PTH) to regulate calcium levels.

• Adrenal Glands: Located above the kidneys; secrete cortisol, aldosterone, epinephrine, and norepinephrine.

• Pineal Gland: Located in the brain; secretes melatonin to regulate sleep-wake cycles.

• Gonads: Ovaries and testes; produce sex hormones (estrogen, progesterone, testosterone).

Hormones and Their Functions

• Pituitary Hormones: ACTH, FSH, LH, GH, PRL, TSH, ADH, oxytocin.

• Thyroid Hormones: T3, T4.

• Parathyroid Hormone: PTH.

• Adrenal Hormones: Cortisol, aldosterone, epinephrine, norepinephrine.

• Pineal Hormone: Melatonin.

• Gonadal Hormones: Estrogen, progesterone, testosterone.

Effects of Aging on the Endocrine System

• Decreased hormone production and sensitivity.

• Associated disorders: Graves Disease, Cushing's Syndrome, Addison's Disease, Acromegaly, Goiter.

Cardiovascular System: Blood

Blood Composition and Functions

Blood is a connective tissue composed of plasma and formed elements (red blood cells, white blood cells, platelets). It transports nutrients, gases, hormones, and waste products throughout the body.

• Plasma: Liquid portion of blood (91.5% water, 7% proteins, 1.5% other solutes).

• Formed Elements: Red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes).

• Functions: Transport, regulation, protection.

Blood Plasma Components

Blood Cell Formation and Types

• Hematopoiesis: Formation of blood cells in red bone marrow.

• Erythropoiesis: Formation of red blood cells, regulated by erythropoietin (EPO).

• Leukopoiesis: Formation of white blood cells.

• Thrombopoiesis: Formation of platelets.

Blood Types and Transfusion

• Blood Types: Determined by antigens (A, B, AB, O) and Rh factor (+/-).

• Transfusion Compatibility: Matching donor and recipient blood types is essential to prevent hemolytic reactions.

• Universal Donor: Type O negative.

• Universal Recipient: Type AB positive.

Hemostasis and Coagulation

• Hemostasis: Process to stop bleeding; involves vascular spasm, platelet plug formation, and coagulation.

• Coagulation Pathways: Intrinsic and extrinsic pathways leading to fibrin clot formation.

• Key Factors: Prothrombin, thrombin, fibrinogen, calcium ions.

Blood Disorders

• Anemia: Reduced oxygen-carrying capacity of blood.

• Hemophilia: Impaired blood clotting.

• Leukemia: Cancer of white blood cells.

• Sickle Cell Disease: Abnormal hemoglobin causing sickle-shaped red blood cells.

The Heart

Heart Structure and Anatomy

The heart is a muscular organ that pumps blood throughout the body. It consists of four chambers (two atria and two ventricles) and is surrounded by the pericardium.

• External Features: Anterior cardiac vein, superior/inferior vena cava, pulmonary arteries/veins, coronary sinus, apex.

• Internal Features: Right/left atrium, right/left ventricle, valves (tricuspid, bicuspid/mitral, pulmonary semilunar, aortic semilunar), septa, papillary muscles, chordae tendineae.

Heart Valves and Blood Flow

• Valves: Ensure unidirectional blood flow; include tricuspid, bicuspid (mitral), pulmonary semilunar, and aortic semilunar valves.

• Blood Flow Pathway: Right atrium → right ventricle → pulmonary artery → lungs → left atrium → left ventricle → aorta → body.

Cardiac Cycle and ECG

• Cardiac Cycle: Sequence of events in one heartbeat; includes systole (contraction) and diastole (relaxation).

• Key Volumes: End-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), cardiac output (CO).

• Formula: $\text{Cardiac Output (CO)} = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)}$

• Electrocardiogram (ECG): Records electrical activity of the heart; segments include P wave, QRS complex, T wave.

Blood Vessel Dynamics

Types of Blood Vessels and Structure

Blood vessels transport blood throughout the body and are classified as arteries, veins, and capillaries. Each type has distinct structural features and functions.

• Arteries: Carry blood away from the heart; thick muscular walls.

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

• Capillaries: Microscopic vessels for exchange of gases, nutrients, and waste.

• Layers: Tunica intima, tunica media, tunica externa.

Blood Vessel Physiology

• Blood Pressure: Force exerted by blood on vessel walls; regulated by cardiac output, vessel diameter, and blood volume.

• Vasoconstriction/Vasodilation: Narrowing/widening of blood vessels to regulate blood flow and pressure.

• Capillary Exchange: Occurs via diffusion, bulk flow, transcytosis, and filtration.

• Venous Return: Assisted by skeletal muscle pump and respiratory pump.

Major Blood Vessels to Know

Additional info: RL = Right/Left; this list is not exhaustive. Refer to course materials for highlighted vessels.

Special Circulatory Features

• Portal Systems: Blood passes through two capillary beds before returning to the heart (e.g., hepatic portal system).

• Peripheral Arterial Pressure (MAP): Mean arterial pressure is a key indicator of blood flow and is affected by cardiac output and resistance.

• Formula: $\text{MAP} = \text{Diastolic BP} + \frac{1}{3}(\text{Systolic BP} - \text{Diastolic BP})$

Mechanisms of Circulation

• Systemic Circulation: Delivers oxygenated blood from the heart to the body and returns deoxygenated blood.

• Pulmonary Circulation: Carries deoxygenated blood from the heart to the lungs and returns oxygenated blood.

• Coronary Circulation: Supplies blood to the heart muscle itself.

Clinical Applications

• Blood Pressure Measurement: Systolic/diastolic values indicate cardiovascular health.

• ECG Interpretation: Used to diagnose arrhythmias, myocardial infarction, and other heart conditions.

• Common Disorders: Hypertension, atherosclerosis, aneurysm, thrombosis.