Endocrine and Reproductive

Hormones

chemical messengers that are released into the blood

hormone controlled processes

• Reproduction

• Growth and development

• Mobilization of body defenses

• Maintenance of much of homeostasis

• Regulation of metabolism

Amino acid based hormones

• proteins

• peptides

• amines

Steroids

made from cholesterol

Prostaglandins

made from highly active lipids that act as local hormones

Hormone action

• Blood transfers hormones to target sites

• Hormones affect only certain tissues or organs (target cells or target organs)

• Target cells must have specific protein receptors

• Hormone binding alters cellular activity

direct gene activation

used by steroid hormones and thyroid hormone

Second-messenger system

used by protein and peptide hormones

Negative feedback mechanisms

• A stimulus or low hormone levels in the blood trigger the release of more hormone.

• Hormone release stops once an appropriate level in the blood is reached.

3 categories of stimuli

• hormonal

• humoral

• neural

Hormonal stimuli

• Most common category of stimulus

• Endocrine organs are activated by other hormones

• Example:

  • Hormones of the hypothalamus stimulate the anterior pituitary to secrete its hormones

Humoral stimuli

• Changing blood levels of certain ions and nutrients stimulate hormone release

  • indicates various body fluids, such as blood and bile

• Examples:

  • Parathyroid hormone and calcitonin are produced in response to changing levels of blood calcium levels

  • Insulin is produced in response to changing levels of blood glucose levels

Neural stimuli

• Nerve fibers stimulate hormone release

• Most are under the control of the sympathetic nervous system

• Examples:

  • Sympathetic stimulation of the adrenal medulla to release epinephrine and norepinephrine

Major endocrine organs

• Hypothalamus

• Pituitary gland

• Pineal gland

• Thyroid gland

• Parathyroid glands

• Thymus

• Adrenal glands

• Pancreas

• Gonads (testes and ovaries)

Pituitary gland

Pea-sized gland that hangs by a stalk from the hypothalamus in the brain

• Often called the “master endocrine gland” because it controls activities of so many other endocrine glands.

Anterior pituitary

glandular tissue

Hypothalamus

• produces releasing hormones and inhibiting hormones.

  • These hormones are released into portal circulation, which connects hypothalamus to anterior pituitary

  • These hormones control the release of anterior pituitary hormones

Oxytocin and Antidiuretic hormone

related in response to nerve impulses from hypothalamus

Posterior pituitary

• Does not make the hormones it releases.

• Stores hormones made by the hypothalamus

made of nervous tissue

two hormones released by posterior pituitary

oxytocin and anitduretic hormone

Oxytocin

• Only released in significant amounts during childbirth and nursing.

• Stimulates contractions of the uterus during labor, sexual relations, and breastfeeding.

• Causes milk ejection (let-down reflex) in a nursing woman.

Antiduretic hormone

• Inhibits urine production (diuresis) by promoting water reabsorption by the kidneys.

• Urine volume decreases, blood volume and pressure increase.

• In large amounts, A D H causes constriction of arterioles, leading to increased blood pressure (the reason why A D H is known as vasopressin)

• Alcohol inhibits ADH secretion

two hormones that affect non-endocrine targets

• growth hormone

• prolactin

Tropic hormones

1. Follicle-stimulating hormone (FSH)

2. Luteinizing hormone (LH)

3. Thyrotropic hormone (TH)

4. Adrenocorticotropic hormone 

   • (ACTH)

Growth hormone

• General metabolic hormone

• Major effects are directed to growth of skeletal muscles and long bones

• Plays a role in determining final body size

• Causes amino acids to be built into proteins

• Causes fats to be broken down for a source of energy

Prolactin

• stimulates and maintains milk production following childbirth

• function in males in unknown

Gonadotropic hormones

Regulate hormonal activity of the gonads

Follicle-stimulation hormone

• Stimulates follicle development in ovaries

• Stimulates sperm development in testes

Luteinizing hormone

• Triggers ovulation of an egg in females

• Stimulates testosterone production in males

Thyroid-stimulation hormone

influences growth and activity of the thyroid gland

Adrenocorticotropic hormone

regulates endocrine activity of the adrenal cortex

Pineal gland

Hangs from the roof of the third ventricle of the brain

Melatonin

secreted by pineal gland

• Believed to trigger the body’s sleep/wake cycle

• Believed to coordinate the hormones of fertility in humans and to inhibit the reproductive system until maturity occurs

Thyroid gland

• Found at the base of the throat, inferior to the Adam’s apple

• Consists of two lobes and a connecting isthmus

• Follicles are hollow structures that store colloidal material

  • Thyroid hormone is derived from this colloid

hormones produced by thyroid gland

• thyroid hormone

• calcitonin

Thyroid hormone

• Major metabolic hormone

• Controls rate of oxidation of glucose to supply body heat and chemical energy (A T P)

• Needed for tissue growth and development

• Composed of two active iodine-containing hormones

  • Thyroxine (T4) - secreted by thyroid follicles

  • Triiodothyronine (T3) - formed from the conversion of T4 at target tissue

Calcitonin

• Decreases blood calcium levels by causing calcium deposition on bone.

• Released in response to rising blood calcium levels.

• Antagonistic to parathyroid hormone.

• Produced by parafollicular cells found between the follicles.

Parathyroid gland

Tiny masses on the posterior of the thyroid gland

Parathyroid hormone

secreted by parathyroid gland

• Most important regulator of calcium ion homeostasis of the blood.

• Hypercalcemic hormone (increases blood calcium levels)

  • Stimulates osteoclasts to remove calcium from bone

  • Stimulates the kidneys and intestine to absorb more calcium

Thymus

• Located in the upper thorax, posterior to the sternum

• Largest in infants and children

• Decreases in size throughout adulthood

Thymosin

produced by thymus

• Matures some types of white blood cells

• Important in developing the immune system

Adrenal glands

sits on top of kidneys

Adrenal cortex

outer glandular region has three layers that produce corticosteroids

• Mineralocorticoids are secreted by outermost layer

• Glucocorticoids are secreted by middle layer

• Sex hormones are secreted by innermost layer

Adrenal medulla

inner neural tissue region

Mineralocorticoids (adrenal cortex)

• Produced in outer adrenal cortex

• Regulate mineral (salt) content in blood, particularly sodium and potassium ions

• Regulate water and electrolyte balance

• Target organ is the kidney

Glucocorticoids (adrenal cortex)

• Produced by middle layer of adrenal cortex

• Promote normal cell metabolism

• Help resist long-term stressors by increasing blood glucose levels (hyperglycemic hormones)

• Anti-inflammatory properties (decrease edema and pain)

Released in response to increased blood levels of ACT H

Sex hormones (adrenal cortex)

• Produced in the inner layer of the adrenal cortex

• Small amounts are made throughout life

• Most of the hormones produced are androgens (male sex hormones), but some estrogens (female sex hormones) are also formed

Adrenal medulla

• Produces two similar hormones (catecholamines)

  1. Epinephrine (adrenaline)

  2. Norepinephrine (noradrenaline)

Epinephrine and Norepinephrine

• These hormones prepare the body to deal with short-term stress (“fight or flight”) by:

  • Increasing heart rate, blood pressure, blood glucose levels

  • Dilating small passageways of lungs

• These events result in more oxygen and glucose in the blood and faster circulation to the organs

Pancreas

• Located in the abdomen, close to stomach

• Mixed gland, with both endocrine and exocrine functions

Insulin

produced by beta cells

• Released when blood glucose levels are high

• Increases the rate of glucose uptake and metabolism by body cells

• Effects are hypoglycemic

Glucagon

produced by alpha cells

• Released when blood glucose levels are low

• Stimulates the liver to release glucose to blood, thus increasing blood glucose levels

• Effects are hyperglycemic

Gonads

• Produce sex cells (exocrine function)

• Produce sex hormones

Ovaries

• Female gonads located in the pelvic cavity

• Produce ova, or eggs

• Produce two groups of steroid hormones

  • Estrogens

  • Progesterone

Testes

• Male gonads suspended outside the pelvic cavity

• Produce sperm

• Produce androgens, such as testosterone

• Responsible for adult male secondary sex characteristics

• Promotes growth and maturation of male reproductive system

• Required for sperm cell production

Estrogens

• Stimulate the development of secondary female characteristics

• Mature the female reproductive organs

Progesterone

• Acts with estrogen to bring about the menstrual cycle

• Helps in the implantation of an embryo in the uterus

• Helps prepare breasts for lactation

non endocrine organs that also secrete hormones

• stomach

• small intestine

• kidneys

• heart

Placenta

• Produces hormones that maintain pregnancy

• Some hormones play a part in the delivery of the baby

• Produces human chorionic gonadotropin (h C G) in addition to estrogen, progesterone, and other hormones

• Human placental lactogen (h P L) prepares the breasts for lactation

• Relaxin relaxes pelvic ligaments and pubic symphysis for childbirth

Gonads

Primary sex organs

• Testes in males

• Ovaries in females

Sperm

male gametes

ova (eggs)

female gametes

Reproductive systems

• Produce offspring via gametes

• Sperm and egg fuse to form a zygote

• Female uterus houses the embryo, and later the fetus, until birth

anatomy of male reproductive system

• Testes

• Duct system

  • Epididymis

  • Ductus (vas) deferens

  • Urethra

Accessory organs of male reproductive system

• seminal glands (vesicles)

• prostate

• bulbourethral glands

External genitalia

• penis

• scrotum

Tunica albuginea

capsule that surrounds each testis

Septa

extensions of the capsule that extend into the testis and divide it into lobules

Seminiferous tubules

1-4 are in each lobule

• Tightly coiled structures

• Function as sperm-forming factories

• Empty sperm into the rete testis

Interstitial cells

in the seminiferous tubules produce androgens such as testosterone

Epididymis

• Highly convoluted tube 6 meters(20 feet) long.

• Found along the posterior lateral side of the testis.

• First part of the male duct system.

• Temporary storage site for immature sperm.

• Sperm mature as they journey through the epididymis.

• During ejaculation, sperm are propelled to the vas deferens.

Ductus (vas) deferens

Runs from the epididymis via the spermatic cord through the inguinal canal and arches over the urinary bladder.

Ampulla

end of the ductus deferent with empires into the ejaculatory duct

Ejaculatory duct

passes through the prostate to merge with the urethra

Ejaculation

smooth muscle in the walls of the ductus deferens create peristaltic waves to squeeze sperm forward.

• causes the internal urethral sphincter to close

  • Prevents urine from passing into the urethra

  • Prevents sperm from entering the urinary bladder

Vasectomy

cutting of the ductus deferent to prevent transportation of stem

• promotes sterility

• male retains secondary sex characteristics

Urethra

• Extends from the base of the urinary bladder to the tip of the penis.

• Carries both urine and sperm

• Sperm enters from the ejaculatory duct

Seminal vesicles

• Located at the base of the bladder

• Produce a thick, yellowish secretion (60% of semen) that contains:

  • Fructose (sugar)

  • Vitamin C

  • Prostaglandins

  • Other substances that nourish and activate sperm

Prostate

• Encircles the upper (prostatic) part of the urethra.

• Secretes a milky fluid

  • Helps to activate sperm

  • Fluid enters the urethra through several small ducts

Bulbourethral glands

• Pea-sized glands inferior to the prostate

• Produce a thick, clear mucus

  • Mucus cleanses the spongy (penile) urethra of acidic urine prior to ejaculation

  • Mucus serves as a lubricant during sexual intercourse

Semen

Milky white mixture of sperm and accessory gland secretions

Components of accessory gland secretions

• Liquid portion acts as a transport medium to dilute sperm

• Sperm are streamlined cellular “tadpoles”

• Fructose provides energy for sperm cells

• Alkalinity of semen helps neutralize the acidic environment of vagina

• Semen inhibits bacteria

Scrotum

• Divided sac of skin outside the abdomen that houses the testes.

• Viable sperm cannot be produced at normal body temperature.

maintains testes at temperature 3^oC lower than body temperature

Penis

Male organ of copulation that delivers sperm into the female reproductive tract.

Regions of the penis

• Shaft

• Glans penis (enlarged tip)

• Prepuce (foreskin)

  • Folded cuff of skin around proximal end

  • Often removed by circumcision

Sperm production

• Begins at puberty and continues throughout life

• Millions of sperm are made every day

Spermatogonia

primitive stem cells that begin the process by divine rapidly

Divison of spermatogonium produces

• Type A daughter cell, a stem cell, that continues the stem cell population

• Type B daughter cell,whichbecomes a primary spermatocyte, destined to undergo meiosis and form four sperm

Meiosis

• Special type of nuclear division that differs from mitosis

• Occurs in the gonads

• Includes two successive divisions of the nucleus (meiosis I & II)

• Results in 4 daughter cells (gametes)

Spermiogenesis

• Spermatids are nonmotile and not functional as sperm

• A sperm has three regions: head, midpiece, tail

• Acrosome sits anterior to the sperm head (nucleus)

  • cap that stores enzymes needed to penetrate the egg

  • take 64-72 days

Testosterone

• Most important hormonal product of the testes

• Stimulates reproductive organ development

• Underlies sex drive

• Causes secondary s

Male secondary sex characteristics

• Deepening of voice

• Increased hair growth

• Enlargement of skeletal muscles

• Increased bone growth and density

Ovaries

Produce eggs (ova) and hormones (estrogen and progesterone)

Each ovary houses ovarian follicles consisting of:

• Oocyte (immature egg)

• Follicle cells—layers of different cells that surround the oocyte

primary follicle

Contains an immature oocytes

Vesicular (Graafian) follicle

growing follicle with a maturing oocyte

Ovulation

the follicle ruptures when the egg is mature and ready to be ejected from the ovary; occurs about every 28 days.

corpus Luteum

transformed ruptured follicle

Uterine (fallopian) tubes

• Form the initial part of the duct system.

• Receive the ovulated oocyte from the ovaries.

• Usual site for fertilization.

• Empty into the uterus.

• Little or no contact between ovaries and uterine tubes.

• Supported and enclosed by the broad ligament.

Infudibulum

Distal, funnel-shaped end