Endocrine and Reproductive Systems: Study Guide (Chapters 16 & 27)

Endocrine System (Chapter 16)

Hormones: Definition and Functions

Hormones are chemical messengers secreted by endocrine glands that regulate the metabolic function of cells throughout the body. They play a crucial role in maintaining homeostasis and coordinating physiological processes.

• Alter plasma membrane permeability or membrane potential.

• Stimulate synthesis of enzymes and other proteins.

• Activate or deactivate enzymes within target cells.

• Induce secretory activity in glands.

• Stimulate mitosis (cell division).

Growth Hormone (GH) and Its Target Cells

Growth Hormone is released from the anterior pituitary gland and acts on multiple tissues:

• Bones

• Cartilage

• Liver

• Muscle

Its primary function is to stimulate growth, cell reproduction, and regeneration.

Gluconeogenesis and Hormonal Control

Gluconeogenesis is the metabolic process by which the liver synthesizes glucose from non-carbohydrate sources (such as amino acids, lactate, and glycerol). This process is vital during fasting or intense exercise.

• Glucagon: Stimulates gluconeogenesis when blood glucose is low.

• Cortisol: Promotes protein breakdown and release of amino acids for gluconeogenesis, especially during stress.

• Epinephrine (adrenaline): Stimulates gluconeogenesis during stress ("fight or flight").

• Insulin: Inhibits gluconeogenesis.

Diabetes Mellitus: Three Cardinal Signs

• Polyuria: Excessive urination

• Polydipsia: Excessive thirst

• Polyphagia: Excessive hunger

Types of Endocrine Stimulation

• Humoral: Triggered by changes in blood composition (e.g., calcium, glucose).

• Neural: Nerve fibers stimulate hormone release (e.g., adrenal medulla).

• Hormonal: Hormones from one gland stimulate another gland (e.g., hypothalamic hormones acting on pituitary).

Second Messenger System

Many hormones, especially amino acid-based hormones, cannot cross the cell membrane. They use a second messenger system to transmit their signal inside the cell:

• Hormone binds to a cell surface receptor.

• This activates a cascade of intracellular events (second messengers such as cAMP).

• Amplifies and relays the signal, resulting in a cellular response.

Functions of Major Hormones (Including Leptin)

• Thyroid-Stimulating Hormone (TSH): Stimulates thyroid gland to release thyroid hormones.

• Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex to release corticosteroids.

• Follicle-Stimulating Hormone (FSH): Stimulates gonads to produce gametes and secrete hormones.

• Luteinizing Hormone (LH): Stimulates gonads to produce sex hormones; triggers ovulation in females.

• Prolactin (PRL): Stimulates milk production in mammary glands after childbirth.

• Growth Hormone (GH): Stimulates growth and cell reproduction.

• Leptin: Produced by adipose tissue; regulates appetite and energy balance.

Target Cells

A target cell is any cell that has a specific receptor for a particular hormone, allowing it to respond to that hormone's signal.

Hypothalamic-Hypophyseal Tract

This is a bundle of nerve fibers connecting the hypothalamus to the posterior pituitary gland, running through the infundibulum. It allows for direct neural communication and hormone transport.

Tropic Hormones of the Anterior Pituitary

• TSH (Thyroid-Stimulating Hormone)

• ACTH (Adrenocorticotropic Hormone)

• FSH (Follicle-Stimulating Hormone)

• LH (Luteinizing Hormone)

Tropic hormones stimulate other endocrine glands to secrete their hormones.

Hypophyseal Portal System

A specialized network of blood vessels connecting the hypothalamus to the anterior pituitary. It allows hypothalamic hormones to reach the anterior pituitary directly, ensuring precise regulation of hormone secretion.

Up-Regulation vs. Down-Regulation

• Up-regulation: Increases the number of receptors on a cell, making it more sensitive to a hormone.

• Down-regulation: Decreases the number of receptors, reducing sensitivity.

Histological Differences: Anterior vs. Posterior Pituitary

Feature	Anterior Pituitary (Adenohypophysis)	Posterior Pituitary (Neurohypophysis)
Structure	Glandular, epithelial cells	Neural tissue, axons from hypothalamus
Function	Synthesizes and releases hormones	Stores and releases hypothalamic hormones (ADH, oxytocin)
Blood Supply	Rich blood supply	Less vascular, more neural

Additional info: These structural differences reflect their distinct roles in hormone production and release.

Reproductive System (Chapter 27)

Functions of Estrogen, Progesterone, and Testosterone

• Estrogen:

  • Promotes female secondary sex characteristics

  • Regulates menstrual cycle and uterine lining growth

  • Supports bone and cardiovascular health

• Progesterone:

  • Prepares and maintains uterine lining for pregnancy

  • Maintains early pregnancy

  • Regulates menstrual cycle (luteal phase)

• Testosterone:

  • Promotes male secondary sex characteristics

  • Stimulates sperm production and libido

  • Supports bone and muscle growth

Testosterone Production in the Testis

Leydig cells (interstitial cells) in the testes produce testosterone in response to LH stimulation.

Pathway of an Ovulated Egg

1. Ovary: Egg released from mature follicle

2. Fimbriae: Finger-like projections sweep egg into uterine tube

3. Infundibulum: Funnel-shaped opening receives egg

4. Ampulla: Widest section, site of most fertilization

5. Isthmus: Narrower part leading to uterus

6. Uterus: Site of implantation or menstruation

Male Glands Producing Semen

• Seminal vesicles: ~60% of semen volume

• Prostate gland: ~30% of semen volume

• Bulbourethral (Cowper's) glands: Contribute mucus and lubrication

Functions of Dartos and Cremaster Muscles

• Dartos muscle: Wrinkles scrotal skin to reduce surface area and conserve heat

• Cremaster muscle: Raises and lowers testes to regulate temperature for optimal sperm production

Hormonal Trigger for Menstruation

A drop in progesterone (and estrogen) triggers the shedding of the uterine lining, resulting in menstruation.

Ovarian and Menstrual Cycle Events

Cycle	Phase	Main Events	Hormone Changes
Ovarian	Follicular	Follicle maturation, estrogen secretion	FSH rises, estrogen rises
Ovarian	Ovulation	Egg released from ovary	LH surge
Ovarian	Luteal	Corpus luteum forms, secretes progesterone	Progesterone rises, estrogen small rise
Menstrual	Menstrual	Endometrial shedding	Progesterone and estrogen drop
Menstrual	Proliferative	Endometrial rebuilding	Estrogen rises
Menstrual	Secretory	Endometrium thickens, glands secrete	Progesterone high

Additional info: If no fertilization occurs, corpus luteum degenerates, hormone levels fall, and menstruation begins.

Physiology of Erection

• Trigger: Sexual arousal activates the parasympathetic nervous system.

• Neural signal: Parasympathetic nerves release nitric oxide, causing smooth muscle relaxation in penile blood vessels.

• Vascular changes: Increased blood flow fills corpus cavernosa (rigidity) and corpus spongiosum (keeps urethra open).

• Result: Penis becomes enlarged and rigid, enabling sexual intercourse.

Functions of the Vagina

• Serves as the birth canal during childbirth

• Receives sperm during intercourse

• Allows for menstrual flow to exit the body

• Provides protection via acidic environment, inhibiting harmful microorganisms

Male Reproductive Duct System

1. Epididymis: Sperm mature and are stored

2. Vas deferens: Transports mature sperm

3. Ejaculatory duct: Formed by joining vas deferens and seminal vesicle duct; passes through prostate

4. Urethra: Delivers sperm and seminal fluid out of the body

Functions of FSH and LH in Males

• FSH (Follicle-Stimulating Hormone):

  • Stimulates Sertoli cells in seminiferous tubules

  • Promotes spermatogenesis (sperm production and maturation)

• LH (Luteinizing Hormone):

  • Acts on Leydig cells in testes

  • Stimulates testosterone production, essential for sperm development and male characteristics

Summary: FSH is crucial for sperm production, while LH is essential for testosterone synthesis.