hormones reproductive cortisol

Class Goals

  • Explore chemical signaling in animals focusing on endocrine processes and hormonal signaling.

  • Use animal reproduction as a primary example.

Understanding Stress

Types of Stress

  • Stress:

    • Definition: Responses to internal or external stressors that threaten well-being.

    • Types:

    • Acute Stress: Single, isolated, or short-term stressors.

    • Chronic Stress: Continuous or repeated long-term stressors.

The Neuroendocrine Stress Systems

Hypothalamic-Pituitary-Adrenal (HPA) Axis

  • Involves interactions between the hypothalamus, the pituitary gland, and the adrenal glands.

  • Components of HPA Axis:

    • Hypothalamus

    • Coticotrophic Releasing Hormone (CRH)

    • Anterior Pituitary releases Adrenocorticotropic Hormone (ACTH)

    • Adrenal Cortex releases Cortisol

Sympathetic Nervous System (SNS)

  • Stimulation of the SNS includes:

    • Epinephrine and Norepinephrine release from adrenal medulla.

    • Increases in heart rate, bronchi relaxation, and glucose release from the liver.

Autonomic Stress Responses

Parasympathetic vs. Sympathetic Responses

  • Parasympathetic Nervous System:

    • Constricts pupils, stimulates salivation, inhibits heart, and stimulates digestive activity.

  • Sympathetic Nervous System:

    • Dilates pupils, inhibits salivation, accelerates heart rate, and inhibits digestive activity.

Responses to Stress

Long-Term Responses

  • Role of Cortisol:

    • Ensures continued glucose availability for the brain during prolonged stress.

    • Known as glucocorticoid for its blood glucose regulation role.

    • Results in a compromise where brain fuel needs are met at the expense of other tissues.

The Hypothalamus and Pituitary

Functions of the Hypothalamus

  • Regulates water balance, stress, hunger, reproduction, thermoregulation, and sleep-wake cycles.

HPA Axis-Mediated Effects

  • Influences mood, emotions, immune responses, thermoregulation, energy storage, and expenditure.

Feedback Inhibition by Glucocorticoids

  • Cortisol:

    • Inhibits ACTH and CRH production, establishing a feedback inhibition loop.

    • Failure of this inhibition can lead to Cushing’s disease, harming protein supplies in the body.

Patterns in Glucocorticoid Release

  • CRH production has a daily rhythm affecting ACTH and cortisol levels.

  • Stress can cause CRH levels to remain elevated, increasing cortisol throughout the day.

Overview of the Hypothalamic-Pituitary Axis

Organization

  • The hypothalamic-pituitary axis consists of two systems (posterior and anterior pituitary).

  • Neurosecretory Cells:

    • Neurons in the hypothalamus that synthesize and release hormones.

Functions of the Pituitary

  • Posterior Pituitary:

    • Stores hormones ADH and oxytocin.

    • Releases ADH for water reabsorption and oxytocin for labor and nursing.

  • Anterior Pituitary:

    • Secretes regulatory hormones influencing several bodily functions including stress response, growth, and reproductive functions.

Human Reproductive Systems

  • Male reproductive system: produces, stores, transports sperm.

  • Female reproductive system: produces eggs, receives sperm, aids early developmental nourishment.

Hormonal Regulation in Reproduction

  • Menstrual Cycle Regulation:

    • Hormones from the pituitary gland and reproductive organs regulate the menstrual cycle via feedback mechanisms.

    • Pregnancy maintenance relies on hormones from the embryo and maternal organs.

Sexual Development in Vertebrates

Key Hormones

  • In Males:

    • Testosterone: Induces early development of the male reproductive tract.

    • Müllerian inhibitory substance: Inhibits female tract development.

  • In Females:

    • Estradiol (an estrogen) is required for female reproductive tract development.

Role in Puberty

  • Hormone surges lead to puberty, modifying physical and emotional attributes aiding reproduction.

Growth in Mammals

Hormonal Regulation

  • Growth hormones (GH) and sex hormones boost cell division and body size while promoting sexual differentiation.

  • GH regulates growth factor levels controlling the cell cycle.

Anatomy of Human Reproductive Organs

Male Reproductive System Components

  1. Spermatogenesis and Storage:

    • Sperm are produced in testes, stored in epididymis.

  2. Accessory Fluids Production:

    • Produced in seminal vesicles, prostate gland, bulbourethral gland, these fluids combine with sperm to form semen.

  3. Transport and Delivery:

    • Vas deferens transports sperm to the ejaculatory duct to the urethra for ejaculation.

Accessory Fluids Functions

Source

Content

Function

Seminal vesicles

Fructose, Prostaglandins

Energy for sperm, stimulate uterine contractions

Prostate gland

Antibiotic compounds

Prevent urinary tract infections

Bulbourethral gland

Citric acid, Alkaline mucus

Lubricate penis, neutralize urethral acidity

Female Reproductive Anatomy

Functions

  1. Egg Production and Transport:

    • Ovaries produce eggs, ovulation sends eggs to oviduct for fertilization.

    • Fertilized eggs are transported to the uterus.

  2. Fetal Development:

    • Development occurs in the uterus; childbirth involves the cervix and vagina.

The Role of Sex Hormones in Reproduction

Male Hormones

  • Testosterone:

    • Produced in Leydig cells; stimulates male reproductive system development.

Female Hormones

  • Estradiol:

    • Produced by ovarian follicles; regulates various reproductive functions.

Hormonal Changes During Reproductive Development

  1. Development of reproductive tract in embryos.

  2. Maturation of reproductive tract from childhood to adulthood.

  3. Regulation of gamete production (spermatogenesis/oogenesis) in adults.

Puberty and Gonadal Hormone Regulation

  • Puberty begins with GnRH release from the hypothalamus.

  • GnRH triggers release of LH and FSH from the pituitary gland, increasing testosterone and estradiol levels.

Roles of LH and FSH

  • In Males:

    • LH stimulates testosterone production in Leydig cells; FSH supports Sertoli cell function crucial for sperm maturation.

  • In Females:

    • LH stimulates theca cells for testosterone, subsequently converted to estrogen by granulosa cells; FSH matures ovarian follicles.

Menstrual Cycle

Overview

  • A monthly cycle in the ovaries and uterus averaging 28 days, includes thickening and shedding of the uterine lining (menstruation).

Phases of the Menstrual Cycle

  • Ovarian Cycle: Follicular phase, ovulation, luteal phase.

  • Uterine Cycle: Menstruation, proliferative phase, secretory phase.

Ovarian Cycle Details

  • Follicular phase: ~14 days, FSH increases lead to dominant follicle maturation.

  • Luteal phase: ~14 days, corpus luteum forms, secretes progesterone for pregnancy readiness.

  • If no fertilization occurs, the corpus luteum degenerates, initiating a new cycle.

Hormonal Changes during the Menstrual Cycle

  • FSH high during the follicular phase, low during luteal; LH maintains steady level with a pre-ovulation spike.

  • Estradiol peaks during the follicular phase; progesterone surges during the luteal phase to prepare the endometrium for a fertilized egg.

Contraceptive Methods

  • Hormone-based contraceptives use synthetic hormones to prevent ovulation (COCP and POP methods).

  • COCP: Contains estrogen and progestin, suppressing ovulation.

  • POP: Contains only progesterone, thickening cervical mucus and thinning uterine lining.

Events of Human Birth

  • Oxytocin, secreted by the pituitary, stimulates uterine contractions, facilitating childbirth.