Endocrine System

Major Endocrine Organs and Their Hormones

The endocrine system consists of glands that secrete hormones directly into the bloodstream to regulate various bodily functions. Each gland produces specific hormones with distinct physiological effects.

• Thyroid gland: Produces thyroxine (T4) and triiodothyronine (T3), which regulate metabolism.

• Parathyroid gland: Produces parathyroid hormone (PTH), which increases blood calcium levels.

• Pituitary gland: Consists of the anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis). The anterior pituitary secretes hormones such as growth hormone (GH), prolactin, and adrenocorticotropic hormone (ACTH). The posterior pituitary releases antidiuretic hormone (ADH) and oxytocin.

• Pancreas: Contains islets of Langerhans that secrete insulin and glucagon to regulate blood glucose levels.

• Adrenal gland: Composed of the cortex (producing corticosteroids: zona glomerulosa - mineralocorticoids, zona fasciculata - glucocorticoids, zona reticularis - androgens) and the medulla (producing catecholamines: epinephrine and norepinephrine).

• Testis: Produces testosterone, responsible for male secondary sexual characteristics.

• Ovary: Produces estrogen and progesterone, regulating female reproductive cycles.

Example: The pancreas releases insulin after a meal to lower blood glucose levels.

Blood and Blood Cells

Types of Blood Cells

Blood is composed of several types of cells, each with specialized functions essential for homeostasis and immunity.

• Erythrocytes (Red Blood Cells): Transport oxygen and carbon dioxide.

• Leukocytes (White Blood Cells): Defend against infection. Types include:

  • Lymphocyte: Involved in immune responses.

  • Neutrophil: Engulfs bacteria and debris.

  • Eosinophil: Responds to parasitic infections and allergies.

  • Basophil: Releases histamine during inflammatory responses.

• Platelet (Thrombocyte): Essential for blood clotting.

Example: Neutrophils increase in number during bacterial infections.

Heart Anatomy

Major Structures of the Heart

The heart is a muscular organ responsible for pumping blood throughout the body. It consists of four chambers and several associated structures.

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

• Valves: Tricuspid valve (right atrioventricular), bicuspid/mitral valve (left atrioventricular), pulmonary valve, aortic valve

• Major vessels: Pulmonary artery, pulmonary vein, aorta, superior and inferior vena cava

• Other structures: Chordae tendineae, papillary muscles, epicardium, myocardium, endocardium

Example: The bicuspid (mitral) valve prevents backflow of blood from the left ventricle to the left atrium.

Major Arteries and Veins

Classification and Identification

Arteries carry blood away from the heart, while veins return blood to the heart. The following table summarizes major arteries and veins in the human body.

Additional info: Arteries generally have thicker walls than veins and carry oxygenated blood (except pulmonary arteries), while veins have valves to prevent backflow and usually carry deoxygenated blood (except pulmonary veins).

Summary Table: Heart Structures

Key Equations

Blood Flow Equation

The flow of blood through a vessel is determined by the pressure difference and resistance:

Where is blood flow, is the pressure difference, and is resistance.

Cardiac Output Equation

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

Where is cardiac output, is heart rate, and is stroke volume.

Conclusion

This study guide covers the identification and function of major endocrine glands, blood cells, heart structures, and major arteries and veins. Understanding these components is essential for mastering human anatomy and physiology.