Endocrine System

Hormones of the Adrenal Gland and Their Functions

The adrenal gland produces several hormones essential for stress response, metabolism, and electrolyte balance.

• Cortisol: Regulates metabolism, immune response, and stress adaptation.

• Aldosterone: Controls sodium and potassium balance, affecting blood pressure.

• Epinephrine & Norepinephrine: Mediate fight-or-flight response, increasing heart rate and blood flow to muscles.

Anatomical and Physiological Connections of the Hypothalamus and Pituitary Glands

The hypothalamus and pituitary glands form a major regulatory axis for endocrine function.

• Hypothalamus: Produces releasing and inhibiting hormones.

• Pituitary Gland: Divided into anterior (adenohypophysis) and posterior (neurohypophysis) lobes; releases hormones in response to hypothalamic signals.

• Connection: The hypothalamic-hypophyseal portal system transports hormones directly from hypothalamus to anterior pituitary.

Functional Classifications of Hormones

Hormones are classified based on their chemical structure and mechanism of action.

• Amino acid-based hormones: Include peptides and proteins (e.g., insulin).

• Steroid hormones: Derived from cholesterol (e.g., cortisol, aldosterone).

• Water-soluble vs. lipid-soluble: Water-soluble hormones act via membrane receptors; lipid-soluble hormones act via intracellular receptors.

Hormones of Calcium Homeostasis

Calcium levels are regulated by three main hormones.

• Parathyroid hormone (PTH): Increases blood calcium by stimulating bone resorption.

• Calcitonin: Lowers blood calcium by inhibiting bone resorption.

• Vitamin D (Calcitriol): Enhances calcium absorption in the gut.

Thymus Gland

The thymus is involved in immune system development.

• Function: Maturation of T-lymphocytes (T-cells).

• Hormones: Thymosin promotes T-cell development.

Homeostasis of Blood Sugar

Blood glucose is regulated by pancreatic hormones.

• Insulin: Lowers blood glucose by promoting uptake into cells.

• Glucagon: Raises blood glucose by stimulating glycogen breakdown.

Cardiovascular System: The Heart

The Heart Anatomy and Conduction System

The heart is a muscular organ with four chambers and a specialized conduction system for coordinated contraction.

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

• Conduction System: Includes the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, bundle branches, and Purkinje fibers.

Blood Flow in the Chambers of the Heart

Blood flows through the heart in a specific sequence, ensuring oxygenation and circulation.

• Right atrium → right ventricle → pulmonary artery → lungs → left atrium → left ventricle → aorta → body

Anatomy of the Walls of the Heart

The heart wall consists of three layers.

• Epicardium: Outer layer, provides protection.

• Myocardium: Middle, muscular layer responsible for contraction.

• Endocardium: Inner layer, lines chambers and valves.

Coronary Cardiac Circuit Anatomy

The coronary circuit supplies blood to the heart muscle itself.

• Coronary arteries: Branch from the aorta to supply oxygenated blood.

• Coronary veins: Drain deoxygenated blood into the right atrium.

Cardiac Cycle Events – 4 Phases

The cardiac cycle consists of four main phases, each corresponding to electrical and mechanical events.

• Atrial systole: Atria contract, forcing blood into ventricles.

• Ventricular systole (first phase): Ventricles contract, AV valves close.

• Ventricular systole (second phase): Semilunar valves open, blood is ejected.

• Ventricular diastole: Ventricles relax, semilunar valves close, blood flows into atria and ventricles passively.

Pulmonary and Systemic Blood Circulation

The heart pumps blood through two main circuits: pulmonary and systemic.

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

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

Cardiac Output Law

Cardiac output is the volume of blood pumped by the heart per minute.

• Formula:

• Normal values: 4-8 L/min in adults.

Stroke Volume Laws

Stroke volume is influenced by preload, afterload, and contractility.

• Preload: Degree of stretch of cardiac muscle before contraction.

• Afterload: Resistance the heart must overcome to eject blood.

• Contractility: Strength of contraction independent of preload.

ECG: All Peaks, Segments, and Intervals

The electrocardiogram (ECG) records electrical activity of the heart.

• P-wave: Atrial depolarization.

• QRS complex: Ventricular depolarization.

• T-wave: Ventricular repolarization.

• PR interval: Time from atrial to ventricular depolarization.

• ST segment: Time between ventricular depolarization and repolarization.

Sinus Rhythm

Sinus rhythm is the normal rhythm of the heart, initiated by the SA node.

• Characterized by regular P waves preceding each QRS complex.

Sounds of the Heart

Heart sounds are produced by valve closures.

• S1: Closure of AV valves (mitral and tricuspid).

• S2: Closure of semilunar valves (aortic and pulmonary).

Athlete ESV, EDV

End-systolic volume (ESV) and end-diastolic volume (EDV) are measures of ventricular volume.

• EDV: Volume of blood in ventricle at end of diastole.

• ESV: Volume of blood remaining after systole.

• Athletes typically have higher EDV and lower ESV due to increased cardiac efficiency.

Blood Vessels and Circulation

Anatomy of the Blood Vessels

Blood vessels include arteries, veins, and capillaries.

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

• Veins: Carry blood toward the heart; thinner walls, valves present.

• Capillaries: Site of exchange between blood and tissues; thin walls.

Blood Pressure Forces Components

Blood pressure is determined by cardiac output and vascular resistance.

• Systolic pressure: Pressure during ventricular contraction.

• Diastolic pressure: Pressure during ventricular relaxation.

• Pulse pressure: Difference between systolic and diastolic.

Blood Pressure Modifying Factors

Several factors influence blood pressure.

• Blood volume

• Vessel diameter

• Heart rate

• Hormones (e.g., epinephrine, angiotensin II)

Blood Pressure Variation Throughout the Body

Blood pressure is highest in arteries and decreases through capillaries and veins.

• Arterial pressure > capillary pressure > venous pressure

Role of SNS and PSNS in BP Regulation

The autonomic nervous system regulates blood pressure.

• Sympathetic Nervous System (SNS): Increases heart rate and vasoconstriction.

• Parasympathetic Nervous System (PSNS): Decreases heart rate.

Mean Arterial Pressure

Mean arterial pressure (MAP) is the average pressure in arteries during one cardiac cycle.

• Formula:

Types of Capillaries

Capillaries are classified by permeability.

• Continuous: Least permeable, most common.

• Fenestrated: Have pores, found in kidneys and intestines.

• Sinusoidal: Most permeable, found in liver and spleen.

Mechanisms of Blood Pressure Regulation

Blood pressure is regulated by neural, hormonal, and renal mechanisms.

• Baroreceptors: Detect changes in pressure.

• Renin-angiotensin system: Increases blood pressure via vasoconstriction and aldosterone release.

• Antidiuretic hormone (ADH): Promotes water retention.

Capillaries Net Filtration Factors

Net filtration in capillaries is determined by hydrostatic and osmotic pressures.

• Formula:

Upper Limb Arteries

Major arteries of the upper limb include:

• Subclavian artery

• Axillary artery

• Brachial artery

• Radial and ulnar arteries

Major Veins

Major veins include:

• Superior and inferior vena cava

• Brachiocephalic vein

• Jugular vein

• Femoral vein

Case Studies

Case Study 1: Thyroid Gland Disorders

Thyroid disorders involve abnormal hormone levels and feedback mechanisms.

• Hormones: T3, T4, and TSH (thyroid-stimulating hormone).

• Feedback: High T3/T4 suppress TSH; low T3/T4 increase TSH.

• Example: Hypothyroidism: low T3/T4, high TSH; Hyperthyroidism: high T3/T4, low TSH.

Case Study 2: Heart Interventricular Defected Wall

A defect in the interventricular wall affects stroke volume and EKG readings.

• Stroke Volume: May decrease due to inefficient pumping.

• EKG: May show abnormal QRS complexes.

Additional info: Defects can lead to mixing of oxygenated and deoxygenated blood, reducing cardiac efficiency.