Comprehensive Study Notes: Cardiovascular, Endocrine, and Lymphatic Systems

Endocrine System

Main Endocrine Organs and Hormones

The endocrine system consists of glands that secrete hormones directly into the bloodstream to regulate various body functions. Understanding the location, structure, and function of these glands is essential in anatomy and physiology.

• Major Endocrine Organs: Pituitary gland, thyroid gland, parathyroid glands, pancreas, adrenal glands, gonads (ovaries and testes).

• Hormones Secreted: Each gland produces specific hormones, e.g., the pituitary secretes growth hormone (GH), thyroid-stimulating hormone (TSH), and antidiuretic hormone (ADH); the thyroid secretes thyroxine (T4) and triiodothyronine (T3).

• Functions: Hormones regulate metabolism, growth, reproduction, and homeostasis.

Example: The pancreas secretes insulin and glucagon to regulate blood glucose levels.

Blood

Formed Elements and Blood Composition

Blood is a connective tissue composed of plasma and formed elements. The formed elements include erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).

• Formed Elements: Identified under a microscope by their shape, size, and staining properties.

• Functions: Erythrocytes transport oxygen, leukocytes defend against pathogens, and platelets aid in clotting.

• Blood Smear: Used to differentiate and identify blood cells.

Example: Neutrophils are the most abundant type of white blood cell and are identified by their multilobed nucleus.

Blood Cell Counts and Hemoglobin

• WBC Count: Used to assess immune function; normal range is 4,000–11,000 cells/μL.

• Hemoglobin: Protein in red blood cells that binds oxygen; measured to assess oxygen-carrying capacity.

• Hematocrit: Percentage of blood volume occupied by red blood cells.

Example: Low hemoglobin may indicate anemia.

Blood Typing and Transfusion

• ABO System: Blood types are determined by the presence of A and B antigens on red blood cells.

• Rh Factor: Presence (+) or absence (–) of Rh antigen; important in transfusion compatibility.

• Transfusion Reactions: Occur when incompatible blood is transfused, leading to agglutination and hemolysis.

Example: Type O negative is the universal donor; type AB positive is the universal recipient.

Heart Conduction

Intrinsic Conduction System

The heart's intrinsic conduction system coordinates the heartbeat through specialized cardiac muscle cells that generate and transmit electrical impulses.

• Main Components: Sinoatrial (SA) node, Atrioventricular (AV) node, Bundle of His, Right and left bundle branches, Purkinje fibers.

• Impulse Pathway: SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers.

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

Example: Heart rate can be calculated from the ECG using the formula:

$\text{Heart Rate (HR)} = \frac{60}{\text{R-R interval (seconds)}}$

Anatomy of the Heart

Heart Chambers and Valves

The heart consists of four chambers: two atria and two ventricles. Valves ensure unidirectional blood flow and prevent backflow.

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

• Valves: Tricuspid, pulmonary semilunar, bicuspid (mitral), aortic semilunar.

• Valve Function: Atrioventricular valves separate atria from ventricles; semilunar valves separate ventricles from major arteries.

Example: The bicuspid (mitral) valve is located between the left atrium and left ventricle.

Circulatory Pathways

• Pulmonary Circuit: Carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium.

• Systemic Circuit: Delivers oxygenated blood from the left ventricle to the body and returns deoxygenated blood to the right atrium.

Example: The aorta is the main artery of the systemic circuit.

Blood Vessels

Structure and Function of Blood Vessels

Blood vessels transport blood throughout the body and are classified as arteries, veins, and capillaries based on structure and function.

• Arteries: Thick muscular walls; carry blood away from the heart.

• Veins: Thinner walls, larger lumen, valves; carry blood toward the heart.

• Capillaries: Thin walls (one cell layer); site of exchange between blood and tissues.

Example: The femoral artery supplies blood to the lower limb.

Feature	Artery	Vein	Capillary
Wall Thickness	Thick	Thin	Very thin
Valves	No	Yes	No
Direction of Blood Flow	Away from heart	Toward heart	Between arteries and veins

Lymphatic System

Components and Functions

The lymphatic system returns excess tissue fluid to the bloodstream and provides immune defense. It consists of lymphatic vessels, lymph nodes, and lymphoid organs.

• Lymphatic Capillaries: Collect interstitial fluid and transport it as lymph.

• Lymphatic Vessels: Carry lymph toward the thoracic duct or right lymphatic duct.

• Lymph Nodes: Filter lymph and house immune cells.

• Lymphatic Organs: Spleen, thymus, tonsils.

Example: The axillary lymph nodes filter lymph from the upper limb.

Blood Pressure and Pulse

Measurement and Interpretation

Blood pressure is the force exerted by circulating blood on vessel walls. Pulse is the rhythmic expansion of arteries with each heartbeat.

• Pulse Points: Radial, carotid, brachial, femoral arteries.

• Blood Pressure Components: Systolic pressure (peak during ventricular contraction), diastolic pressure (lowest during relaxation).

• Normal Values: Systolic: 90–120 mmHg; Diastolic: 60–80 mmHg.

• Measurement: Sphygmomanometer is used to measure blood pressure.

Example: Blood pressure is recorded as systolic/diastolic (e.g., 120/80 mmHg).

$\text{Blood Pressure} = \frac{\text{Force}}{\text{Area}}$

Additional info: Academic context and definitions have been expanded for clarity and completeness.