Endocrine System, Blood, and Circulatory Pathways: Study Guide for Anatomy & Physiology

Endocrine System

Endocrine Hormones

The endocrine system consists of glands that secrete hormones directly into the bloodstream to regulate various bodily functions. Hormones act on specific target organs or tissues and play critical roles in growth, metabolism, reproduction, and homeostasis.

• Hypothalamus: Produces regulatory hormones that control the release of hormones from the anterior pituitary.

  • Antidiuretic Hormone (ADH)

  • Oxytocin (OXT)

  • Regulatory Hormones:

    • Thyrotropin-Releasing Hormone (TRH)

    • Corticotropin-Releasing Hormone (CRH)

    • Gonadotropin-Releasing Hormone (GnRH)

    • Growth Hormone-Releasing Hormone (GHRH)

    • Growth Hormone-Inhibiting Hormone (GHIH)

    • Prolactin-Releasing Factor (PRF)

    • Prolactin-Inhibiting Hormone (PIH)

• Anterior Pituitary: Releases hormones that regulate other endocrine glands and various physiological processes.

  • Thyroid Stimulating Hormone (TSH)

  • Adrenocorticotropic Hormone (ACTH)

  • Follicle Stimulating Hormone (FSH)

  • Luteinizing Hormone (LH)

  • Growth Hormone (GH)

  • Prolactin (PRL)

  • Melanocyte-Stimulating Hormone (MSH)

• Posterior Pituitary: Stores and releases hormones produced by the hypothalamus.

  • Antidiuretic Hormone (ADH) – also known as Vasopressin (VP)

  • Oxytocin (OXT)

• Thyroid:

  • Calcitonin (CT)

  • Thyroxine (T4)

  • Triiodothyronine (T3)

• Parathyroid:

  • Parathyroid Hormone (PTH)

• Adrenal Cortex:

  • Zona Glomerulosa: Mineralocorticoids (Aldosterone)

  • Zona Fasciculata: Glucocorticoids (Cortisol)

  • Zona Reticularis: Androgens

• Adrenal Medulla:

  • Epinephrine (E)

  • Norepinephrine (NE)

• Pancreas:

  • Glucagon

  • Insulin

• Testes & Ovaries:

  • Androgens (Testes)

  • Estrogens (Ovaries)

• Pineal:

  • Melatonin

Example: The hypothalamus releases TRH, which stimulates the anterior pituitary to secrete TSH, leading to thyroid hormone production.

Endocrine Histology

Histological identification of endocrine tissues is essential for understanding hormone production and glandular structure.

• Thyroid:

  • Follicular cells

  • Parafollicular cells (C cells)

• Adrenal:

  • Adrenal cortex: zona glomerulosa, zona fasciculata, zona reticularis

  • Adrenal medulla

• Pancreas:

  • Pancreatic islets (islets of Langerhans)

  • Acinar cells

• Ovary:

  • Follicular cells

  • Follicular fluid

  • Oocyte

  • Graafian (tertiary) follicle

• Testis:

  • Leydig cells

  • Sertoli cells

  • Seminiferous tubules

  • Germinal epithelium

  • Lumen

Example: Pancreatic islets contain alpha cells (secrete glucagon) and beta cells (secrete insulin).

Blood and Blood Vessels

Components of Blood

Blood is a connective tissue composed of plasma and formed elements. It performs transport, regulatory, and protective functions.

• Erythrocytes (Red Blood Cells): Transport oxygen and carbon dioxide; produced in bone marrow.

• Leukocytes (White Blood Cells): Defend against pathogens; types include neutrophils, eosinophils, basophils, monocytes, and lymphocytes.

• Thrombocytes (Platelets): Involved in blood clotting.

• Plasma: Liquid matrix containing water, proteins, nutrients, hormones, and waste products.

Example: Neutrophils are the most abundant type of leukocyte and are essential for phagocytosis of bacteria.

Blood Typing

Blood typing is based on the presence or absence of specific antigens on the surface of erythrocytes and corresponding antibodies in plasma.

• Antigen: A molecule on the surface of a cell that can trigger an immune response.

• Antibody: A protein produced by the immune system that binds to a specific antigen.

• ABO System: Blood types are A, B, AB, and O, determined by the presence of A and/or B antigens.

• Rh Factor: Presence (+) or absence (−) of the Rh antigen.

Example: A person with type A blood has A antigens on erythrocytes and anti-B antibodies in plasma.

Blood Vessel Structure

Blood vessels transport blood throughout the body and are classified based on their structure and function.

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

• Veins: Carry blood toward the heart; have thinner walls and valves.

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

• Structural Differences: Tunica media (muscle layer), tunica intima (inner layer), tunica externa (outer layer).

Example: The aorta is the largest artery, while the vena cava is the largest vein.

Systemic (Peripheral) Circulatory System Pathways

Overview of Circulatory Pathways

The systemic circulatory system delivers oxygenated blood from the heart to the body and returns deoxygenated blood to the heart. Students should be able to label all arteries and veins in the 11 major pathways.

• Arteries: Carry oxygen-rich blood from the left ventricle to tissues.

• Veins: Return oxygen-poor blood to the right atrium.

• Pathways: Include head/neck, upper limb, thoracic, abdominal, pelvic, and lower limb circuits.

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

Cat Organs and Blood Vessels

Identification in Laboratory Specimens

Students should be able to identify major organs and blood vessels in cat specimens, as listed in laboratory manuals.

• Organs: Heart, lungs, liver, kidneys, etc.

• Blood Vessels: Major arteries and veins corresponding to human anatomy.

Example: The renal artery supplies blood to the kidneys in both cats and humans.

Lymphatic System

Functions and Components

The lymphatic system returns interstitial fluid to the bloodstream, absorbs fats from the digestive tract, and provides immune defense.

• Functions: Fluid balance, fat absorption, immune response.

• Lymphatic Vessels: Transport lymph; include capillaries, vessels, trunks, and ducts.

• Lymphoid Organs: Thymus, red bone marrow, lymph nodes, spleen, tonsils, MALT (Mucosa Associated Lymphoid Tissue).

• Lymphocytes: White blood cells involved in adaptive immunity.

• Innate Immunity: Non-specific defense mechanisms (e.g., barriers, phagocytes).

• Adaptive Immunity: Specific immune responses involving B and T lymphocytes.

Example: The spleen filters blood and removes old erythrocytes and pathogens.

Flow of Lymph

Lymph flows from peripheral tissues through lymphatic vessels and is eventually returned to venous blood flow.

• Interstitial fluid enters lymphatic capillaries.

• Lymph is transported through vessels and nodes.

• Lymph drains into the thoracic duct or right lymphatic duct, which empty into the subclavian veins.

Example: Lymph from the lower limbs drains into the thoracic duct.

HTML Table: Major Endocrine Glands and Their Hormones

Gland	Hormone(s)	Main Function(s)
Hypothalamus	ADH, OXT, Regulatory Hormones	Regulation of pituitary hormone release, water balance, uterine contraction
Anterior Pituitary	TSH, ACTH, FSH, LH, GH, PRL, MSH	Growth, metabolism, reproduction, stress response
Posterior Pituitary	ADH, OXT	Water reabsorption, uterine contraction, milk ejection
Thyroid	T3, T4, CT	Metabolism, calcium regulation
Parathyroid	PTH	Calcium regulation
Adrenal Cortex	Aldosterone, Cortisol, Androgens	Electrolyte balance, stress response, sex characteristics
Adrenal Medulla	Epinephrine, Norepinephrine	Fight-or-flight response
Pancreas	Insulin, Glucagon	Blood glucose regulation
Testes	Androgens	Male sex characteristics
Ovaries	Estrogens	Female sex characteristics
Pineal	Melatonin	Regulation of circadian rhythms

Key Equations and Concepts

• Blood Flow Equation: $Q = \frac{\Delta P}{R}$ Where $Q$ is blood flow, $\Delta P$ is the pressure difference, and $R$ is resistance.

• Osmotic Pressure Equation: $\Pi = iMRT$ Where $\Pi$ is osmotic pressure, $i$ is the van 't Hoff factor, $M$ is molarity, $R$ is the gas constant, and $T$ is temperature.

Additional info: Some details, such as the specific laboratory manual pages and Blackboard resources, were inferred as references for further study and not included in these notes.