Introduction to Endocrine System Lab: Anatomy & Physiology II

Endocrine System Overview

Introduction

The endocrine system is a network of glands that produce and secrete hormones to regulate various bodily functions. In Anatomy & Physiology II lab, students will learn to identify major endocrine glands, understand their histological features, and recognize the hormones they produce and their physiological effects.

• Endocrine glands secrete hormones directly into the bloodstream.

• Hormones are chemical messengers that regulate growth, metabolism, reproduction, and homeostasis.

• Key tasks include identifying glands on models and slides, knowing cell types, hormones, targets, and effects of hormone imbalances.

Major Endocrine Glands

Pituitary Gland

The pituitary gland, often called the "master gland," regulates many other endocrine glands. It is divided into anterior and posterior lobes, each with distinct cell types and hormone functions.

• Anterior pituitary (adenohypophysis): Contains acidophils, basophils, and chromophobes.

• Posterior pituitary (neurohypophysis): Stores and releases hormones produced by the hypothalamus.

• Key hormones: Growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), oxytocin, antidiuretic hormone (ADH).

• Histology: Acidophils stain pink, basophils stain blue/purple, chromophobes are pale.

Thyroid Gland

The thyroid gland is located in the neck and regulates metabolism through hormone secretion.

• Follicular cells secrete thyroid hormones (T3 and T4).

• Parafollicular cells secrete calcitonin, which lowers blood calcium levels.

• Histology: Follicles filled with colloid, surrounded by follicular cells.

Parathyroid Glands

Small glands located on the posterior aspect of the thyroid gland, essential for calcium homeostasis.

• Chief cells secrete parathyroid hormone (PTH), which increases blood calcium levels.

• Oxyphil cells (function not well understood).

Pineal Gland

The pineal gland is a small, pinecone-shaped structure in the brain that regulates circadian rhythms.

• Pinealocytes secrete melatonin, derived from serotonin.

• Melatonin regulates sleep-wake cycles and may influence puberty and antioxidant production.

• Pineal sand (calcium deposits) is a landmark in brain imaging.

Adrenal Glands

Located atop the kidneys, adrenal glands consist of two regions: cortex and medulla, each producing different hormones.

• Adrenal cortex: Three layers (zona glomerulosa, zona fasciculata, zona reticularis) produce corticosteroids.

• Adrenal medulla: Produces catecholamines (epinephrine and norepinephrine).

• Functions: Regulate stress response, metabolism, blood pressure, and electrolyte balance.

Pancreas

The pancreas has both exocrine and endocrine functions, crucial for digestion and blood glucose regulation.

• Acinar cells (exocrine): Produce digestive enzymes.

• Pancreatic islets (Islets of Langerhans) (endocrine):

  • Alpha cells: Secrete glucagon (raises blood glucose).

  • Beta cells: Secrete insulin (lowers blood glucose).

Thymus

The thymus is large in children and shrinks with age; it is vital for immune system development.

• Thymic hormones (thymulin, thymopoietins, thymosins) aid in lymphocyte maturation.

• Acts as a paracrine organ in immune response.

Gonads: Ovaries and Testes

Gonads produce sex hormones essential for reproduction and secondary sexual characteristics.

• Ovaries: Produce estrogen and progesterone.

• Testes: Interstitial cells produce testosterone.

• Functions: Regulate reproductive organ maturation, gamete production, and secondary sexual traits.

Hormones: Functions and Imbalances

General Actions of Hormones

• Hormones act on specific target organs to regulate physiological processes.

• Imbalances (too high or too low) can cause disease or dysfunction.

Examples of Hormone Imbalances

• Hypothyroidism: Low thyroid hormone, causes fatigue, weight gain.

• Hyperthyroidism: High thyroid hormone, causes weight loss, increased metabolism.

• Diabetes mellitus: Insulin deficiency or resistance, leads to high blood glucose.

• Cushing's syndrome: Excess cortisol, causes obesity, hypertension.

Microscopic Anatomy: Histology Tips

How to Study Histology Slides

• Observe and draw representative images.

• Label unique features, cell types, and hormones produced.

• Identify distinguishing characteristics for each gland.

Summary Table: Major Endocrine Glands, Hormones, and Functions

Gland	Main Cell Types	Hormones Produced	Main Functions
Pituitary (Anterior)	Acidophils, Basophils, Chromophobes	GH, TSH, ACTH, FSH, LH, PRL	Growth, metabolism, reproduction
Pituitary (Posterior)	Neurosecretory cells	Oxytocin, ADH	Water balance, childbirth
Thyroid	Follicular, Parafollicular cells	T3, T4, Calcitonin	Metabolism, calcium regulation
Parathyroid	Chief, Oxyphil cells	PTH	Calcium homeostasis
Pineal	Pinealocytes	Melatonin	Sleep-wake cycles
Adrenal Cortex	Zona glomerulosa, fasciculata, reticularis	Aldosterone, Cortisol, Androgens	Electrolyte balance, stress response
Adrenal Medulla	Chromaffin cells	Epinephrine, Norepinephrine	Fight-or-flight response
Pancreas	Alpha, Beta cells	Glucagon, Insulin	Blood glucose regulation
Thymus	Thymic epithelial cells	Thymulin, Thymopoietins, Thymosins	Immune system development
Ovaries	Follicular, Luteal cells	Estrogen, Progesterone	Female reproduction
Testes	Interstitial (Leydig) cells	Testosterone	Male reproduction

Key Equations

• Blood Glucose Regulation:

$\text{Blood Glucose Level} = \text{Glucose Intake} - \text{Insulin Action} + \text{Glucagon Action}$

• Calcium Homeostasis:

$\text{Blood Calcium Level} = \text{Intestinal Absorption} + \text{Bone Resorption} - \text{Renal Excretion}$

Clinical Applications

• Understanding endocrine gland structure and function is essential for diagnosing and treating hormonal disorders.

• Histological identification aids in recognizing pathological changes in glandular tissue.

Additional info: Some details about cell types and hormone functions were inferred from standard Anatomy & Physiology textbooks to ensure completeness.