BIO 201 Lecture Exam 1

Functions of the Endocrine System

• Regulates growth, development, and metabolism

• Maintain homeostasis of blood composition and volume

• Controls digestive processes

• Controls innume response

• Controls reproductive processes

Similarities of Nervous & Endocrine Systems

• Both maintain homeostasis

• Both communicate via chemicals that bind to receptors

Differences of Nervous & Endocrine Systems

Nervous

• Uses neurotransmitters released at synapses

• Effects are almost immediate & short-lasting

Endocrine

• Uses hormones released into the bloodstream

• Effects are in seconds to days & longer-lasting

Endocrine Glands

• Ductless - Internal Secretion

• Hormones act only on target cells with receptors for them

• Connective tissue framework

Exocrine Glands

• Secrete into ducts or tubes that lead to a body surface

• Deliver their products directly to a specific site

Endocrine Organs

glands with a solely endocrine function

Examples of Endocrine Organs

• Pituitary Gland

• Pineal Gland

• Thyroid Gland

• Parathyroid Glands

• Adrenal Glands

Organs with Endocrine Cell Clusters

Function is not solely endocrine; include:

• Hypothalamus

• Skin

• Thymus

• Heart

• Liver

• Stomach

• Pancreas

• Small Intestine

• Adipose Connective Tissue

• Kidneys

• Gonads

Hormones

chemical messengers secreted by endocrine glands that regulate functions of other cells.

• Have widespread effects throughout the body

• Continue circulating the blood until taken up by a target cell or broken down and deactivated

Factors Affecting Levels of Circulating Hormones

1. Hormone Release

   1. Positively correlated with blood concentration

2. Hormone Elimination

   1. Negatively correlated with blood concentration

   2. Occurs in multiple ways

3. Half-Life of Hormone

   1. Water-Soluble = shorter half-life: ~few minutes

   2. Lipid-Soluble = longer half-life b/c carrier proteins protect them

Target Cells

contain specific protein receptors to which specific hormones bind

Receptors

3-D shapes highly specific for hormone or chemical messenger they bind

• Can be embedded in plasma membrane

• Or

• Reside in cytosol or nucleus of target cell

Up-Regulation

process by which target cells produce a greater number of receptors in response to a temporary increase in hormone level of blood

Down-Regulation

process by which target cells decrease number of receptors in response to prolonged exposure to a high level of hormone in the blood

Classes of Hormones

• Steroid Hormones

• Biogenic Amines

• Proteins

Steroid Hormones

class of hormones that are lipid-soluble and derived from cholesterol

Types of Steroid Hormones

• Gonadal Steroids (estrogen, progesterone, testosterone)

• Adrenal Cortex Steroids (cortisol)

• Calictrol (sometimes classified in this group; more accurately a sterol though)

Biogenic Amines

class of hormones that are modified amino acids and water-soluble

• Exception: thyroid hormone is nonpolar and lipid-soluble due to a pair of tyrosines

Types of Biogenic Amines

• Catecholamines (epinephrine, norepinephrine)

• Thyroid Hormone

• Melatonin

Proteins

class of most hormones which are water-soluble chains of amino acids; most hormones are a part of this class.

Types of Protein Hormones

• Antidiuretic Hormone (ADH)

• Insulin

• Glucagon

• Growth Hormone (GH)

• Erythropoietin

Types of cell Signaling

• Endocrine

• Paracrine

• Autocrine

Endocrine Cell Signaling

hormones secreted into blood and taken up by target tissue of a different cell type than the signaling cell

Paracrine Cell Signaling

chemicals secreted into the extracellular space to affect nearby, but different types of cells than the signaling cell

Autocrine Cell Signaling

chemicals secreted into interstitial fluid which elicits effects from the same cell or same cell type as the signaling cell

Local Hormones

hormones not secreted into the bloodstream, but instead into surrounding tissue

• Example: Eicosanoids

Eicosanoids

local hormone formed from fatty acids within the phospholipid bilayer through an enzymatic cascade

• Example: prostaglandins

• Function in diverse physiological and pathological systems

  • Mounting or inhibiting inflammation

  • Allergy

  • Fever & other immune responses

  • Regulating the abortion of pregnancy & normal childbirth

  • Contribute to the perception of pain

  • Regulate cell growth

  • Control blood pressure

  • Modulate the regional flow of blood to tissues

Prostaglandins

example of an eicosanoid that stimulates pain and inflammatory response

Aspirin and Other Nonsteroidal Anti-Inflammatory Drugs

can be used to block prostaglandin formation reliving pain and inflammation

Ways Hormones are Eliminated from Bloodstream

• Enzymatic degradation in liver cells

• Uptake by target cells

• Excretion by kidneys

Half-Life

time necessary to reduce a hormone’s concentration to half of its original level

• Example - testosterone = 12 days

Lipid-Soluble Hormones

small, nonpolar, and hydrophobic hormones that can diffuse across target cell membranes to reach receptors in the cytosol or nucleus

Hormone-Receptor Complex

complex formed from the binding of a lipid-soluble hormone to a receptor. Complex eventually binds to DNA causing changes in transcription & translation which may have structural or metabolic effects on the cell

Hormone-Response Element (HRE)

point on DNA strand that a hormone-receptor complex is able to bind to influence transcription & translation

Water-Soluble Hormones

hydrophilic, polar hormones that cannot diffuse across membranes and therefore must attach to receptors in the membrane of target cell to induce a signal transduction pathway to induce change.

First Messenger

hormone that initiates a signal transduction pathway by binding

G-Protein

internal membrane protein that binds a guanine nucleotide; binding of the first messenger turns GDP into GTP, an active form which activates membrane enzymes to catalyze the formation of a second messenger

Second Messenger

a chemical made by membrane enzymes in a signal transduction pathway which modifys cellular activity in someway

Possible Effects of Hormones

• Stimulating secretion from endocrine or exocrine cell

• Activating or inhibiting enzymes

• Stimulating or inhibitng cell division (mitosis or meiosis)

• Opening or closing ion channels in plasma membrane —> alters membrane potential (electrical charge)

• Activating or inhibiting transcription of genes that code for RNA or proteins (gene expression)

Types of Endocrine Stimulation

• Hormonal Stimulation

• Humoral Stimulation

• Nervous System Stimulation

Hormonal Stimulation

release of one hormone causes the release of a different hormone

Humoral Stimulation

changes in nutrient or ion levels of the blood causes the release of hormones

Nervous System Stimulation

stimulation of the nervous system causes the release of hormones

Regulation of Hormone Secretion

• Stimulus - regulated physiological variable deviates from its normal range

• Receptor - detects the deviation of the variable

• Control Center - often the endocrine cell; increases or decreases its secretion of a particular hormone

• Effector/Response - hormone triggers a response in its target cells that moves conditions toward the normal range

• Homeostatis Range - as the variable returns to normal, feedback to the control center decreases the effector response

Tropic Hormones

hormones that act on other glands and regulate their hormone secretion

Non-Tropic Hormones

do not cause hormone secretion; instead, control bodily function directly by stimulating or inhibiting target cells

Trophic Hormones

hormones which induce growth in target cells

Example of Trophic Hormone

TSH is both tropic and trophic; causes release of thyroid hormone from the thyroid gland and also causes growth of the thyroid gland. Reason a goiter is a symptom of thyroid issues.

Hypothalamus

• Part of the brain, contains neurons

• One of the largest endocrine organs

• Closely associated with the pituitary gland

  • Some neurons enter the posterior pituitary and secrete hormones

  • Other neurons secrete hormones into a network of blood vessels that travel into the anterior pituitary, controlling its secretion of hormones

• Homeostatic Functions:

  • Thirst

  • Hunger

  • Fluid Balance

  • Body Temperature

  • Sleep/Wake Cycle

  • Certain Reproductive Functions

Anterior Pituitary (Adenohypophysis)

• “Adeno” meaning gland

• Receives blood flow and hormones

• Releases its own hormones

Posterior Pituitary (Neurohypophysis)

• “Neuro” since it is made up of nervous tissue

• Does not produce or release any of its own hormones; instead hormones of the hypothalamus are released into this area

Hypothalamohypophyseal Portal System

network of blood vessels connecting the hypothalamus and anterior pituitary. Consists of:

• Primary Plexus

• Hypophyseal Portal Veins

• Secondary Plexus

Hormones of the Posterior Pituitary

• Not made; just released into this part

• Two neurohormones stored in synaptic vesicles in axon terminals

  • Antidiuretic Hormone (ADH)

  • Oxytocin

Antidiuretic Hormone (ADH)

• Neurohormone made by the hypothalamus and released into the posterior pituitary

• Osmoreceptors send a signal to the brain when the water content of the blood is low or high

  • Low Water Content —> Increase in ADH —> High volume of water reabsorbed by kidneys —> low urine output & very concentrated urine

  • High Water Content —> Decrease in ADH —> Low volume of water reabsorbed by kidneys —> high urine output & dilute urine

Diabetes Insipidus

• Condition caused by an abnormal lack of ADH secretion or activity

• Symptoms

  • Frequent Urination

  • Extreme Thirst

  • Dehydration

• Treatment

  • Synthetic ADH (if secretion is the issue)

  • Antidiuretics or low-sodium diet (if kidneys are the issue)

Oxytocin

• Neurohormone made by the hypothalamus but released into the posterior pituitary

• Functions

  • Muscle contraction of the uterine walls during childbirth

  • Milk ejection during lactation (Milk let-down reflex)

• Target cells

  • Mammary glands of breast tissue

  • Smooth muscle of the uterus

Milk Let-Down Reflex

reflex in nursing mothers which exhibits a positive feedback loop

• Stimulation of pressoreceptors in nipples by suckling sends impulses to hypothalamus

• Hypothalamus sends impulses to posterior pituitary to release oxytocin

• Stimulated myoepithelial cells of breasts to contract

• Alveolar glands respond by releasing milk through the ducts of the nipple

• Continues until the infant stops suckling

Releasing Hormone

hormones produced by hypothalamus capable of accelerating secretion of given hormone by anterior pituitary

Stimulating Hormone

a hormone produced by the anterior pituitary that stimulates another gland to produce another hormone

Inhibiting Hormone

a hormone that inhibits the secretion of another hormone.

• Example: Prolactin-Inhibiting Hormone (PIH) of the hypothalamus

Releasing Hormones of the Hypothalamus

• Thyrotropin-Releasing Hormone (TRH)

• Prolactin-Releasing Hormone (PRH)

• Gonadotropin-Releasing Hormone (GnRH)

• Corticotropin-Releasing Hormone (CRH)

• Growth Hormone-Releasing Hormone (GHRH)

Inhibiting Hormones of the Hypothalamus

• Prolactin-Inhibiting Hormone (PIH)

• Growth Hormone-Inhibiting Hormone (GHIH)

Tropic Hormones of Anterior Pituitary

• Thyroid-Stimulating Hormone (TSH)

• Prolactin (PRL)

• Follicle-Stimulating Hormone (FSH) & Luteinizing Hormone (LH)

• Growth Hormone (GH)

• Adenocorticotropic Hormone (ACTH)

Thyrotropin-Releasing Hormone (TRH)

releasing hormone of the hypothalamus that induces the anterior pituitary to release TSH

Prolactin-Releasing Hormone (PRH)

releasing hormone of the hypothalamus that stimulates the anterior pituitary to release PRL

Gonadotropin-Releasing Hormone (GnRH)

releasing hormone of the hypothalamus that stimulates the anterior pituitary to release FSH & LH

Corticotropin-Releasing Hormone

releasing hormone of the hypothalamus that stimulates the anterior pituitary to release ACTH.

Growth Hormone-Releasing Hormone (GHRH)

releasing hormone of the hypothalamus that stimulates the anterior pituitary to release GH.

• Amount released depends on person’s age (decreases with age), time of day (increasing during sleeping hours), nutrient levels, stress, and excercise

Prolactin-Inhibiting Hormone (PIH)

inhibiting hormone of the hypothalamus that represses the anterior pituitary from releasing PRL

Growth Hormone-Inhibiting Hormone (GHIH)

inhibiting hormone of the hypothalamus that represses the release of GH from the anterior pituitary

Thyroid-Stimulating Hormone (TSH)

hormone of the anterior pituitary that stimulates growth of thyroid gland and release of thyroid hormone (TH)

Prolactin (PRL)

hormone of the anterior pituitary that stimulates growth of the mammary glands and increases milk production

Follicle-Stimulating Hormone (FSH) & Luteinizing Hormone (LH)

hormones of the anterior pituitary that act on the gonads to stimulate the development of their respective gametes and release sex hormones

Growth Hormone (GH)

hormone of the anterior pituitary that stimulates release of IGF’s from the liver, which synergistically act on all body tissues, especially cartilage bone, muscle, and adipose tissue to stimulate growth

Adenocorticotropic Hormone (ACTH)

hormone of the anterior pituitary that stimulates the adrenal cortex to release glucocorticoids (such as cortisol)

Gigantism

disorder caused by too much growth hormone which causes big people

Acromegaly

growth hormone disorder that affect flat bones of the face, flattening and enlarging the face

Pituitary Dwarfism

lack of growth hormone which causes little people

Anatomy of the Thyroid Gland

• Left & Right Lobes connected at the midline by a narrow isthmus

• Highly vascularized

• Composed of microscopic follicles

• Cellular Structure

  • Protein-rich, gelatinous colloid in the middle, surrounded by follicle cells

  • Parafollicular cells around colloid & follicle cells

Parafollicular Cells

cells of the thyroid that release calcitonin hormone leading to a colloid

Follicle Cells

cuboidal epithelial cells that surround colloid and produce and release TH

Parathyroid Glands

Typically 3 to 5 separate glands on posterior surface of the thyroid

• Secrete parathyroid hormone (PTH) from chief cells

• Regulate calcium ion levels

  • Important for bone health; helps prevent conditions such as osteoporosis

Chemical Structure of Thyroid Hormone

• Amino acid core bound to 3 (triiodothyroxine, T₃) or 4 (thyroxine, T₄) iodine atoms

• T₄ commonly converted to T₃ to target issues. (Both physiologically active, but T₃ moreso)

• T₃ and T₄ are more hydrophic than other monoamines, allowing them to enter the target cell’s nucleus

Functions of Thyroid Hormone

• Regulation of Metabolic Rate & Thermoregulation

  • Sets basal metabolic rate by increasing the rate at which cells carry out metabolic reactions

  • Heat generated through metabolism: critical for core body temp homeostasis

    • Cold stimulates an increase in metabolic rate, and heat decreases metabolic rate

• Promotion of Growth & Development

  • Required for normal bone growth, muscle growth, and nervous system development

  • Deficiency leads to birth defects

• Synergism with Sympathetic Nervous System

  • Up-regulates production of receptors for sympathetic neurotransmitters

    • Helps regulate BP, heart rate, and other sympathetic activities

Regulation of Thyroid Hormones

• Stimulus: decreased levels of free T₃ or T₄ or exposure to cold

• Receptors in the hypothalamus detect change

• First-Tier Control: Hypothalamus releases TRH

• Second-Tier Control: Anterior pituitary releases TSH

• Third-Tier Control: Thyroid gland produces & secretes T₃ and T₄ + grows & develops

• Effects

  • Increased levels of T₃ & T₄ in blood = increased metabolic rate

Parathyroid Hormone (PTH)

• Secreted by chief cells of the parathyroid gland

• Secreted in response to declining calcium ion levels

• Effects:

  • Increases release of calcium ions from bone by stimulating osteoclast activity

    • Breaks down bone to free up calcium ions

  • Acts on kidneys to convert inactive vitamin D into its active form, calcitrol (Vitamin D₃)

    • Increases absorption of calcium from diet

  • Increases reabsorption of calcium ions in kidneys

Calcitonin

• Produced and secreted by parafollicular cells

• Released when calcium levels increase above normal (hypercalcemia)

• Primary target is osteoclast cells

  • Inhibits their activity

    • Allows osteoblast activity

Structure of Adrenal Glands

• Located on top of the kidneys

• Roughly pyramid-shaped

• Produces two types of hormones

  • Steroid Hormones (Aldosterone, Cortisol, & Sex Hormones)

  • Catecholamines (Epinephrine & Norepinephrine)

• Divided into two sections

  • Adrenal Cortex

  • Adrenal Medulla

Adrenal Cortex

• Subdivided into 3 zones

  • Zone Glomerulosa (Outermost)

  • Zone Fasciculata (Middle Zone)

  • Zone Reticularis (Innermost Zone)

• Secretes mineralcorticoids, glucocorticoids, & androgenic steroids

Zone Glomerulosa

• Outermost Zone of Adrenal Cortex

• Densely packed cells

• Secretes mineralocorticoid hormones (ex. aldosterone)

Zone Fasciculata

• Middle zone of adrenal cortex

• Cells stacked in columns

• Secretes glucocorticoids (ex. cortisol)

Zone Reticularis

• Innermost zone of adrenal cortex

• Thin layer of cells; arranged loosely in clusters

• Secrete androgenic steroids (gonadocorticoids)

Aldosterone

• Regulates the concentration of certain electrolytes (Na⁺ & K⁺) in body fluids, blood pH, and blood pressure

• Aldosterone released

  • Na⁺ & Cl^- move from kidneys to blood to maintain electrolyte balance. H₂O follows, helping maintain BP

  • K⁺ transported from blood to the kidneys

  • H⁺ transported from blood to the kidneys

• K⁺ and H⁺ are both excreted in urine

Cortisol (Hydrocortisone)

• Most potent glucocorticoid in the body

• Receptors located throughout the body = widespread effect

• Effects:

  • Gluconeogenesis in the liver

  • Release of amino acids from muscle tissue

  • Release of fatty acids from adipose tissue

  • Suppresses immune cells & inflammatory response

• Regulated by negative feedback loop

  • Stimulus - morning hours, stress, and sympathetic NS

Cushing Syndrome

disorder caused by chronic exposure to excessive glucocorticoid hormones

• Symptoms

  • Obesity

  • Hypertension

  • Hirsuitism (excess male-pattern hair growth)

  • Kidney Stones

  • Menstrual Irregularities

Addison Disease

disorder that develops when the adrenal glands fail

• Chronic shortage of glucocorticoids and sometimes mineralocorticoids

• May develop from lack of ACTH or lack of response to ACTH

• Symptoms

  • Weight Loss

  • Fatigue

  • Weakness

  • Hypotension

  • Skin Darkening

• Treatment

  • Therapy with oral corticosteroids

Androgenic Steroids

steroid sex hormones that affect reproductive organs as well as other tissues

• Adrenal cortex synthesizes these in small quantities in both genders

  • Largely byproducts of cortisol synthesis

• Can be converted in circulation to the androgen testosterone or the female hormone estrogen

• Same general effects as those made by the gonads

Adrenal Medulla

• Inner section of an endocrine gland

• Made up of chromaffin cells

• Secretes epinephrine & norepinephrine

Chromaffin Cells

• Cells that make up the adrenal medulla

• Nervous tissue origins

• Secrete mostly epinephrine directly into the bloodstream

• Stimulated by

  • Sympathetic neurons to release

  • or

  • By acetylcholine released from preganglionic sympathetic neurons

Epinephrine

• Hormone that mediates sympathetic responses to stressful situations (Fight, Flight, or Freeze Response)

  • Way to reach cells not innervated by the sympathetic NS

• Physiological Effects

  • Increases heart rate and force of heart contraction

  • Dilates bronchioles

  • Constricts blood vessels supplying skin, digestive organs, and urinary organs (Increasing blood pressure)

  • Dilates blood vessels supplying skeletal muscles

  • Dilates pupils

  • Decreases digestive & urinary functions