Hormones and Signal Transduction

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Questions and Answers

What type of hormone is mainly composed of polypeptide chains and is water-soluble?

Amino Acid Hormone

Steroid Hormone

Peptide Hormone (correct)

Lipid Hormone

Which of the following is NOT a factor that affects the up-regulation or down-regulation of hormone receptors?

Time of day (correct)

Genetic mutation

Diet

Body temperature

What mechanism allows steroid hormones to initiate transcription in the nucleus?

Diffusing through the cell membrane (correct)

Inducing a cascade effect

Directly interacting with DNA

Binding to surface cell receptors

Which type of feedback system typically reduces hormone secretion when the desired effect is achieved?

Negative feedback Signup and view all the answers

Hormones act as first messengers in signal transduction. What is the role of second messengers in this process?

They relay signals within the cell. Signup and view all the answers

Which hormone classification typically ends with 'ol' or 'one'?

Steroid Hormone Signup and view all the answers

What is the sequence of events that occurs after a water-soluble hormone attaches to a G-protein linked receptor?

G-protein is activated, followed by activation of adenylyl cyclase. Signup and view all the answers

Which type of receptors do lipid-soluble hormones primarily attach to?

Cytoplasmic receptors Signup and view all the answers

What type of hormones are derived from tyrosine and tryptophan?

Amino Acid Hormones Signup and view all the answers

The sensitivity of a cell to a hormone can change based on the number of receptors present. What happens when there are too many circulating hormones?

Receptor down-regulation occurs. Signup and view all the answers

What effect does the second messenger cAMP have within the cell?

It activates protein kinase A (PKA) to influence metabolic pathways. Signup and view all the answers

Which of the following hormone signaling mechanisms involves direct attachment to ion channels?

Ion channel receptors Signup and view all the answers

What is the role of Janus kinase 2 (JAK2) in enzyme-linked receptor signaling?

It is phosphorylated and activated as a second messenger. Signup and view all the answers

In signal transduction, what is the first messenger in the context of enzyme-linked receptors?

Leptin Signup and view all the answers

Which hormone attachment leads to changes in membrane potential by directly opening ion channels?

Neurotransmitters Signup and view all the answers

Where is the hypothalamus located in relation to the thalamus?

Below the thalamus Signup and view all the answers

What role do the nuclei in the hypothalamus serve?

They produce and store hormones. Signup and view all the answers

How does the hypothalamus maintain homeostasis?

By managing temperature, food intake, and emotional responses. Signup and view all the answers

Which of the following hormones is synthesized and released by the posterior pituitary gland?

Oxytocin Signup and view all the answers

What happens if there is an injury to the hypothalamus?

It can disrupt temperature regulation. Signup and view all the answers

What are the components of the pituitary gland?

Posterior and anterior portions Signup and view all the answers

Which neurotransmitters play a role in the release of hormones from the posterior pituitary gland?

Glutamate and GABA Signup and view all the answers

What is often referred to as the master gland of the endocrine system?

Pituitary gland Signup and view all the answers

Where are the hormone-producing nuclei located within the hypothalamus?

At the base of the brain, near the pituitary gland Signup and view all the answers

What triggers the secretion of antidiuretic hormone (ADH) from the posterior pituitary?

Increased serum osmolarity Signup and view all the answers

Which receptors does ADH bind to in smooth muscle to cause vasoconstriction?

V1 receptors Signup and view all the answers

What is a characteristic of the Syndrome of Inappropriate Antidiuretic Hormone (SIADH)?

High circulating ADH levels Signup and view all the answers

Which condition is associated with excess water loss and increased serum osmolality?

Diabetes Insipidus (DI) Signup and view all the answers

What causes dilutional hyponatremia in SIADH?

Excessive water retention Signup and view all the answers

In Diabetes Insipidus, what leads to polyuria?

Insufficient ADH production Signup and view all the answers

Which type of Diabetes Insipidus is caused by renal tubular resistance to ADH?

Nephrogenic DI Signup and view all the answers

What symptom is likely when serum sodium levels drop to 120-130 mEq/L?

Nausea and abdominal cramps Signup and view all the answers

Which of the following is NOT a cause of Diabetes Insipidus?

Increased concentrations of vasopressin Signup and view all the answers

What condition is indicated by high ADH levels without appropriate feedback to the hypothalamus?

Syndrome of Inappropriate Antidiuretic Hormone (SIADH) Signup and view all the answers

Study Notes

Lecture Hall Timeline

1:30-2:15: PollEv questions and focused review
2:20-3:05: Meet with group, work on case/questions
3:05-3:15: Break
3:15-4:15: Review case/questions, submit assignment
4:20: Class end

Questions & Review

A & P: Hormones, Hypothalamus, Pituitary (Anterior/Posterior), Adrenals (Cortex/Medulla), Thyroid, Parathyroid, Pineal
Pathophysiology: DI & SIADH, Hyperthyroidism & thyroid storm, Cushing's & adrenal insufficiency, DKA/HHS
Group work: Endocrine case

Hormones

Chemical substance produced by specialized cells, transported to distant cells, exerting regulatory effects
Structural categories: water-soluble or lipid-soluble
Classified as: Peptide hormones, Amino acid hormones, Steroid hormones
Peptide Hormone: Water-soluble polypeptide chains, bind onto effector cell receptors, inducing a cascade effect, ends with "in" or "ine"
Amino Acid Hormone: Water-soluble, derived from tyrosine and tryptophan, enzymatic conversion, bind to receptors, ends with "in" or "ine"
Steroid Hormone: Lipid-soluble, crosses effector cell membrane, binds to cytoplasmic receptor, passage into the nucleus, binding to DNA, initiating transcription, ends with "ol" or "one"

Hormone Regulation

Hormone secretion patterns: Diurnal, Pulsatile & Circadian, Levels of circulating substrates
Feedback systems: Negative & positive, Endocrine/Hormonal factors, Chemical/Humoral factors, Neural control

Hormone Receptors

Sensitivity determined by receptor number, hormone affinity and conditions (pH, body temp)
Can increase (up-regulation) or decrease (down-regulation) in response to hormone levels
Diet, pH, temperature, and mutations can influence up/down-regulation

Hormone Signal Transduction

Hormones are the first messengers
Water-soluble hormones attach to plasma membrane receptors: G-protein linked receptors, ion channel receptors, enzyme-linked receptors
Lipid-soluble hormones attach to: Plasma membrane receptors, Cytoplasmic receptors, Nuclear membrane receptors

G-Protein Linked Receptors

Hormones attach to plasma membrane receptors
Activated G-protein reacts with GTP
GTP activates plasma membrane adenylyl cyclase enzyme
Adenylyl cyclase converts ATP to cAMP, a second messenger
cAMP activates protein kinase (PKA)
PKA activates several intracellular enzymes
Affects transcription results in synthesis of proteins, producing target cell response

Ion Channel Receptors

Hormones/neurotransmitters open ion channels by direct attachment or attachment to g-protein linked channels
Changes membrane potential

Enzyme Linked Receptors

Hormone attachment activates several enzyme systems
Example (Leptin): Leptin (first messenger) attaches to plasma membrane enzyme receptor; Janus kinase 2 (JAK2), a second messenger is phosphorylated, activated; signal transduction & activator (STAT) proteins are phosphorylated and activated, transcription of genes for protein synthesis, other enzyme systems are activated

Steroid Hormone Action

Steroid hormone enters target cell
Hormone binds to receptor, induces conformational change
Hormone-receptor complex binds to DNA, induces start of transcription
Amplification of signal occurs, many mRNAs are produced
Each transcript further translated, amplifying the signal

Hypothalamus

Located below thalamus, above midbrain (ventral diencephalon), connected to the pituitary gland
Composed of nuclei (clusters of neuron cell bodies), axons connecting nervous and endocrine systems
Nuclei produce hormones, hormone stimulating/inhibiting factors for transportation to pituitary gland

Hypothalamic Function

Maintains homeostasis: temperature regulation, food & water intake, sexual behavior, daily cycles, emotional/stress responses, metabolism, growth

Pituitary Gland (Hypophysis)

Pea-sized gland attached to hypothalamus
Receives hormones for storage/release (from hypothalamus)
Stimulatory/inhibitory factors, promote/inhibit synthesis/release of hormones
Master gland controlling most other endocrine glands
Partitioned into anterior and posterior portions

Posterior Pituitary (Neurohypophysis)

Receives peptide hormones produced in hypothalamic nuclei
Oxytocin & ADH/arginine-vasopressin are synthesized and packaged in vesicles with carrier proteins
Vesicles move down pituitary stalk, stored in posterior pituitary gland
Glutamate & GABA neurotransmitters can stimulate/inhibit hormone release

Posterior Pituitary Hormones

Oxytocin: Stimulates uterus contraction, milk ejection, positive feedback mechanism
ADH (Vasopressin): Formation/concentration of urine (facultative water reabsorption), response to increased blood osmolarity, regulates water reabsorption

Antidiuretic Hormone

Antidiuretic hormone (ADH, or arginine vasopressin) regulates water reabsorption in the collecting tubules of the kidneys
ADH secretion from the posterior pituitary triggered by increased serum osmolarity
Binds to V2 receptors, stimulating aquaporin channels' translocation for water reabsorption in the renal distal tubules/collecting ducts
Maintaining blood osmolarity

Hypothalamic-Pituitary Alterations

SIADH: Excessive ADH, without appropriate feedback from hypothalamus; excess water retention, dilutional hyponatremia
Diabetes Insipidus (DI): Deficient ADH; often caused by inadequate ADH, renal tubular collecting ducts' insensitivity or excessive fluid intake -Excessive water loss leads to increased serum osmolality, decreased urine output

Thyroid Gland

Located in the anterior neck, lying over trachea
Composed of right and left lobes, connected by isthmus
Follicular cells surround follicular lumen, trapping iodine, synthesizing and storing thyroid hormones
C cells secrete calcitonin
Synthesis of thyroid hormones: Iodide absorbed from GIT, iodide travels into follicular cells and is converted to iodine, and then attached to thyroglobulin for T3 and T4 (with 2 iodine and 3 iodine respectively)

Thyroid Hormones

T3 (triiodothyronine) is more biologically potent than T4 (thyroxine)
T4 is converted to T3 peripherally in liver and kidneys
Small amounts of T4 deiodinated to inactive reverse T3
Thyroid hormones regulate many bodily functions

Secretion and Conversion of T4 & T3

Hypothalamus releases TRH to pituitary
Pituitary releases TSH to thyroid
TSH triggers thyroid peroxidase to produce T3/T4
93% of T4 and 7% of T3 is used immediately
Conversion of T4 to T3 in liver (60%)

Factors Affecting T3 to T4 Conversion

Contributing factors: nutrients (iron, iodine, tyrosine), vitamins; inhibiting factors: stress, infection, toxins; factors to increase conversion T4 to T3 - selenium; zinc; factors to increase conversion T4 to RT3—Stress, trauma, low calorie diet, inflammation, certain medications

Functions of Thyroid Hormones

Act via nuclear receptors in target cells
Global metabolic and development effects
T4 and T3 either diffuse or are carried through the lipid portion of the cell membrane or are carried through a transporter
Hormones bind to mitochondrial and nuclear surfaces (T3 has highest affinity)
- Binding to receptors alters transcription of specific genes (suppresses or activates)

Functions of Thyroid Hormones (Metabolism)

Increased gluconeogenesis /glucose hepatic production, available necessary amino acids, glycerol, specific enzymes
Increased glycolysis/available free glucose,
Increased proteolysis in muscle, amino acids available for gluconeogenesis, increased protein synthesis
Increased lipolysis/triglyceride degradation in adipose tissue, glycerol and fatty acids, lipogenesis

Functions of Thyroid Hormones (Cardiovascular)

Systemic arteriole dilation, decreased SVR/afterload
Increased circulating blood volume/preload, dilated vessels, stimulates renin-angiotensin system
Increases heart rate, regulating action potential duration and repolarization currents, and regulates genes in pacemaker cells
Increases force of contraction

Feedback Mechanisms of the Hypothalamic Pituitary Axis (HPA)

Increased levels of thyroid hormones signal the hypothalamus to stop secreting TSH.
Most feedback systems are negative where increased levels of a substance inhibit further release of stimulating factors.

Alterations in Thyroid Function (Hyperthyroidism)

Graves disease: Primary autoimmune; TSH-producing adenomas
Goiter: Enlargement of thyroid gland; TSH-secreting pituitary adenoma can progress to thyroid storm.

Alterations in Thyroid Function (Thyroid Storm/Crisis)

Sudden, dramatic increase in circulating thyroid hormones.
May result from undiagnosed or poorly controlled hyperthyroidism, precipitated by stress, infection, surgery.

Thyroid Storm Diagnosis

Includes measurements for thermoregulatory dysfunction, gastrointestinal-hepatic dysfunction, cardiovascular dysfunction, mental dysfunction etc.

The Adrenal Gland

Anatomically associated with each kidney, sharing the same blood supply
Two layers: cortex (3 layers of cells) and medulla.

Adrenal Cortex Hormones (Mineralocorticoids)

Zona glomerulosa synthesizes and secretes mineralocorticoids—Regulated by the Renin-Angiotensin-Aldosterone system which responds to Na+ & H2O depletion or hyperkalemia
Angiotensin II stimulates aldosterone secretion binds to receptors in distal renal nephrons epithelial cells and stimulates Na⁺ and water retention, K⁺ and H⁺ depletion

Adrenal Cortex Hormones (Glucocorticoids)

Zona fasciculata synthesizes and secretes glucocorticoids which are stimulated by ACTH from the anterior pituitary.
Effects: Metabolic, anti-inflammatory/immunosuppressive, and growth-suppressing.

Hormones of the Adrenal Medulla

Chromaffin cells (pheochromocytes) store epinephrine and norepinephrine in secretory granules, working closely with the sympathetic nervous system to respond to stress
Sympathetic preganglionic nerve fibers stimulated by stress to secrete acetylcholine
Chromaffin cells depolarize, leading to exocytosis of granules, release of epinephrine and norepinephrine
Catecholamines bind to alpha and beta receptors.

Adrenal Gland Vascular Supply

Adrenal blood supply flows into cortical arteries then branches into capillary networks (cortex & medulla), draining into a central medullary vein.
This arrangement exposes the medulla to high concentrations of glucocorticoids.

Effects of a & b Receptor Stimulation

Activation of beta receptors increases myocardial force and rate of contraction, and may lead to arrhythmias.
Activation of alpha receptors causes vasoconstriction
Activation of beta receptors causes bronchial dilation and a decrease in airway resistance.

Stress Response

Short-term stress: involves activation of sympathetic nervous system and adrenal medulla, resulting in increased heart rate, blood pressure, and release of catecholamines
Prolonged stress: activates hypothalamic-pituitary-adrenal (HPA) axis, and involves the release of cortisol.

Adrenal Abnormalities (Cushing Syndrome/Disease)

Cushing syndrome: Clinical manifestations from chronic exposure to high cortisol levels from various causes (e.g., pituitary tumor, exogenous corticosteroids)
- Symptoms/signs vary and can include changes in body shape and distribution of fat, high blood pressure, high blood sugar and susceptibility to infections

Cushing's Disease/Syndrome

Possible causes: ACTH-dependent pituitary tumors (70%), adrenal tumors, unknown cause (15%); exogenous causes: taking medications containing corticosteroids (15%)
Signs and symptoms of excess cortisol, (e.g., upper body obesity, buffalo hump, full moon face, thin extremeties, fragile skin bruising)

Adrenal Insufficiency

Decrease of circulating cortisol and/or aldosterone, lack of stimulation from hypothalamus and pituitary gland
Inability of adrenal glands to produce cortisol and aldosterone
Causes include autoimmune disorders, tuberculosis, fungal infections.
Symptoms include fatigue, postural dizziness, syncope etc, decreased libido, amenorrhea.

Insulin

Secreted by beta cells in response to elevated blood glucose
Stimulates liver to convert glucose to glycogen
Promotes increased potassium levels in cells
GLUT4 transporters are stored in cytoplasmic vesicles, and released into the cell membrane to allow glucose transport

Glucagon

Secreted by alpha cells in response to low blood glucose
Stimulates glycogenolysis in the liver release of glucose into the blood; used for energy.
Promotes gluconeogenesis: the synthesis of glucose from non-carbohydrate sources
Used for energy during periods of fasting.

Types of Diabetes

Type 1: usually autoimmune, short history, acute onset, not typically overweight, rare, insulin deficiency, requires insulin at diagnosis, often random diagnosis
Type 2: usually older age, insidious onset, often overweight, insulin resistance, common, diet and lifestyle change can reverse it
Gestational: first detected during pregnancy, often overweight, insulin resistance, placental hormones, becoming more common, diet and lifestyle plus medications affecting growing baby, family history

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Description

Test your knowledge on hormones, their types, and how they interact with receptors in the body. This quiz covers water-soluble and lipid-soluble hormones, feedback mechanisms, and the role of second messengers in signal transduction. Answer questions about hormone actions, classifications, and regulatory mechanisms.