BIO 094 Chapter 9 Lecture

The Endocrine System : The Endocrine System

The Endocrine System : The Endocrine System Second-messenger system of the body Uses chemical messengers (hormones) that are released into the blood Hormones control several major processes Reproduction Growth and development Mobilization of body defenses Maintenance of much of homeostasis Regulation of metabolism

Hormone Overview : Hormone Overview Hormones are produced by specialized cells Cells secrete hormones into extracellular fluids Blood transfers hormones to target sites These hormones regulate the activity of other cells

The Chemistry of Hormones : The Chemistry of Hormones Hormones are classified chemically as Amino acid–based, which includes Proteins Peptides Amines Steroids—made from cholesterol Prostaglandins—made from highly active lipids

Mechanisms of Hormone Action : Mechanisms of Hormone Action Hormones affect only certain tissues or organs (target cells or target organs) Target cells must have specific protein receptors Hormone-binding alters cellular activity

Effects Caused by Hormones : Effects Caused by Hormones Changes in plasma membrane permeability or electrical state Synthesis of proteins, such as enzymes Activation or inactivation of enzymes Stimulation of mitosis Promotion of secretory activity

The Chemistry of Hormones : The Chemistry of Hormones Two mechanisms in which hormones act Direct gene activation Second-messenger system

Direct Gene Activation (Steroid Hormone Action) : Direct Gene Activation (Steroid Hormone Action) Diffuse through the plasma membrane of target cells Enter the nucleus Bind to a specific protein within the nucleus Bind to specific sites on the cell’s DNA Activate genes that result in synthesis of new proteins

Slide 9 : Figure 9.1a Nucleus Cytoplasm Steroidhormone Receptor protein Hormone-receptorcomplex DNA mRNA Newprotein Plasmamembraneof targetcell

Second-Messenger System (Nonsteroid Hormone Action) : Second-Messenger System (Nonsteroid Hormone Action) Hormone binds to a membrane receptor Hormone does not enter the cell Sets off a series of reactions that activates an enzyme Catalyzes a reaction that produces a second-messenger molecule Oversees additional intracellular changes to promote a specific response

Slide 11 : Figure 9.1b Cytoplasm Nonsteroidhormone (firstmessenger) Enzyme Receptorprotein Secondmessenger Effect on cellular function,such as glycogenbreakdown Plasmamembraneof target cell ATP cAMP

Major Endocrine Glands and Hormones : Major Endocrine Glands and Hormones Table 9.1 (1 of 4)

Major Endocrine Glands and Hormones : Major Endocrine Glands and Hormones Table 9.1 (2 of 4)

Major Endocrine Glands and Hormones : Table 9.1 (3 of 4) Major Endocrine Glands and Hormones

Major Endocrine Glands and Hormones : Table 9.1 (4 of 4) Major Endocrine Glands and Hormones

Control of Hormone Release : Control of Hormone Release Hormone levels in the blood are mostly maintained by negative feedback A stimulus or low hormone levels in the blood triggers the release of more hormone Hormone release stops once an appropriate level in the blood is reached

Hormonal Stimuli of Endocrine Glands : Hormonal Stimuli of Endocrine Glands Figure 9.2a Most common stimuli Endocrine glands are activated by other hormones Examples: Anterior pituitary hormones

Humoral Stimuli of Endocrine Glands : Humoral Stimuli of Endocrine Glands Figure 9.2b Changing blood levels of certain ions stimulate hormone release Humoral indicates various body fluids such as blood and bile Examples: Parathyroid hormone Calcitonin Insulin

Neural Stimuli of Endocrine Glands : Figure 9.2c Neural Stimuli of Endocrine Glands Nerve impulses stimulate hormone release Most are under the control of the sympathetic nervous system Examples include the release of norepinephrine and epinephrine by the adrenal medulla

Major Endocrine Organs : Major Endocrine Organs Pituitary gland Thyroid gland Parathyroid glands Adrenal glands Pineal gland Thymus gland Pancreas Gonads (Ovaries and Testes) Hypothalamus

Location of Major Endrocrine Organs : Location of Major Endrocrine Organs Figure 9.3

Pituitary Gland : Pituitary Gland Size of a pea Hangs by a stalk from the hypothalamus in the brain Protected by the sphenoid bone Has two functional lobes Anterior pituitary—glandular tissue Posterior pituitary—nervous tissue Often called the “master endocrine gland”

Hormones of the Anterior Pituitary : Hormones of the Anterior Pituitary Six anterior pituitary hormones Two affect non-endocrine targets Growth hormone Prolactin Four stimulate other endocrine glands (tropic hormones) Thyroid-stimulating hormone (thyrotropic hormone) Adrenocorticotropic hormone Two gonadotropic hormones

Hormones of the Anterior Pituitary : Hormones of the Anterior Pituitary Figure 9.4

Hormones of the Anterior Pituitary : Hormones of the Anterior Pituitary 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

Hormones of the Anterior Pituitary : Hormones of the Anterior Pituitary Growth hormone (GH) disorders Pituitary dwarfism results from hyposecretion of GH during childhood Gigantism results from hypersecretion of GH during childhood Acromegaly results from hypersecretion of GH during adulthood

Hormones of the Anterior Pituitary : Hormones of the Anterior Pituitary Gigantism Figure 9.5a

Hormones of the Anterior Pituitary : Hormones of the Anterior Pituitary Dwarfism Figure 9.5b

Pituitary–Hypothalamus Relationship : Pituitary–Hypothalamus Relationship Hormonal release is regulated by releasing and inhibiting hormones produced by the hypothalamus Hypothalamus produces two hormones These hormones are transported to neurosecretory cells of the posterior pituitary Oxytocin Antidiuretic hormone The posterior pituitary is not strictly an endocrine gland, but does release hormones

Hormones of the Posterior Pituitary : Hormones of the Posterior Pituitary Oxytocin Stimulates contractions of the uterus during labor, sexual relations, and breastfeeding Causes milk ejection in a nursing woman Antidiuretic hormone (ADH) Inhibits urine production by promoting water reabsorption by the kidneys In large amounts, causes vasoconstriction leading to increased blood pressure

Hormones of the Posterior Pituitary : Hormones of the Posterior Pituitary Figure 9.6

Thyroid Gland : Thyroid Gland Figure 9.7a

Thyroid Gland : Thyroid Gland Thyroid hormone Major metabolic hormone Composed of two active iodine-containing hormones Thyroxine (T4)—secreted by thyroid follicles Triiodothyronine (T3)—conversion of T4 at target tissues Calcitonin Decreases blood calcium levels by causing its deposition on bone

Thyroid Gland : Thyroid Gland Figure 9.7b

Thyroid Gland : Thyroid Gland Figure 9.8

Parathyroid Glands : Parathyroid Glands Tiny masses on the posterior of the thyroid Secrete parathyroid hormone (PTH) Stimulate osteoclasts to remove calcium from bone Stimulate the kidneys and intestine to absorb more calcium Raise calcium levels in the blood

Hormonal Regulation of Calcium in Blood : Hormonal Regulation of Calcium in Blood Figure 9.10

Adrenal Glands : Adrenal Glands Sit on top of the kidneys Two regions Adrenal cortex—outer glandular region has three layers Mineralocorticoids secreting area Glucocorticoids secreting area Sex hormones secreting area Adrenal medulla—inner neural tissue region

Hormones of the Adrenal Cortex : Hormones of the Adrenal Cortex Figure 9.11

Hormones of the Adrenal Cortex : Hormones of the Adrenal Cortex Mineralocorticoids (mainly aldosterone) Regulate mineral content in blood Regulate water and electrolyte balance Glucocorticoids (including cortisone and cortisol) Promote normal cell metabolism Help resist long-term stressors Sex hormones Small amounts- Mostly androgens (male sex hormones) are made but some estrogens (female sex hormones) are also formed

Roles of the Hypothalamus and Adrenal Glands in the Stress Response : Roles of the Hypothalamus and Adrenal Glands in the Stress Response Figure 9.13

Hormones of the Adrenal Medulla : Hormones of the Adrenal Medulla Produces two similar hormones (catecholamines) Epinephrine (adrenaline) Norepinephrine (noradrenaline) 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

Pancreatic Islets : Pancreatic Islets The pancreas is a mixed gland and has both endocrine and exocrine functions The pancreatic islets produce hormones Insulin—allows glucose to cross plasma membranes into cells from beta cells Glucagon—allows glucose to enter the blood from alpha cells These hormones are antagonists that maintain blood sugar homeostasis

Pancreatic Islets : Pancreatic Islets Figure 9.14b–c

Slide 45 : Figure 9.15 Insulin-secretingcells of the pancreasactivated; releaseinsulin into theblood Elevatedblood sugarlevels Stimulus:rising bloodglucose levels(e.g., aftereating fourjelly doughnuts) Rising bloodglucose levelsreturn blood sugarto homeostatic setpoint; stimulus forglucagon releasediminishes Blood glucoselevels declineto set point;stimulus forinsulin releasediminishes Stimulus:declining bloodglucose levels(e.g., afterskipping a meal) Low bloodsugar levels Glucagon-releasingcells of pancreasactivated;release glucagoninto blood; targetis the liver Uptake of glucosefrom blood is en-hanced in mostbody cells Liver breaks downglycogen stores andreleases glucose tothe blood Liver takes upglucose and storesit as glycogen Homeostasis: Normal blood glucoselevels (90 mg/100ml) Imbalance Imbalance

Thymus Gland : Thymus Gland Located posterior to the sternum Largest in infants and children Produces thymosin Matures some types of white blood cells Important in developing the immune system

Gonads : Gonads Ovaries Produce eggs Produce two groups of steroid hormone Estrogens Progesterone Testes Produce sperm Produce androgens, such as testosterone

Hormones of the Ovaries : Hormones of the Ovaries Estrogens Stimulate the development of secondary female characteristics Mature female reproductive organs Promote breast development Regulate menstrual cycle 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

Hormones of the Testes : Hormones of the Testes Produce several androgens Testosterone is the most important androgen Responsible for adult male secondary sex characteristics Promotes growth and maturation of male reproductive system Required for sperm cell production

Developmental Aspects of the Endocrine System : Developmental Aspects of the Endocrine System Most endocrine organs operate smoothly until old age Menopause is brought about by lack of efficiency of the ovaries Problems associated with reduced estrogen are common Growth hormone production declines with age Many endocrine glands decrease output with age