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Questions and Answers

What initiates the release of anterior pituitary hormones?

Nervous stimulation

Release of hormones from the adrenal gland

Hormones from the hypothalamus (correct)

Hormones from the final target organs

What is the relationship between permissiveness and hormone function?

One hormone can function independently without the presence of other hormones.

One hormone makes another hormone's effects stronger by enhancing its action. (correct)

Permissiveness describes the situation when hormones from the target organs inhibit hormone release.

One hormone directly inhibits another hormone's function.

What does synergism refer to in hormone action?

One hormone decreases the effectiveness of another hormone.

One hormone acts only in the absence of another.

Hormones work against each other.

Multiple hormones enhance the same effect on a target cell. (correct)

Which part of the brain serves as a major link between the nervous and endocrine systems?

Hypothalamus Signup and view all the answers

How are the hypothalamus and pituitary gland connected?

Infundibulum Signup and view all the answers

If one hormone opposes the action of another, this relationship is referred to as what?

Antagonism Signup and view all the answers

What type of hormone release is specifically caused by another hormone?

Hormonal stimuli Signup and view all the answers

What is the primary function of hormones released from the anterior pituitary?

To stimulate other endocrine glands to secrete hormones Signup and view all the answers

What is the primary role of the anterior lobe of the pituitary?

Receives signals from the hypothalamus and sends out hormones Signup and view all the answers

What happens to hypothalamic hormones after they are secreted?

They travel through portal veins to the anterior pituitary Signup and view all the answers

Which hormones are secreted by the anterior pituitary in response to hypothalamic releasing hormones?

GH, TSH, ACTH, FSH, LH, PRL Signup and view all the answers

What structure connects the primary and secondary capillary plexuses in the portal system of the pituitary?

Veins Signup and view all the answers

What is the function of Follicle-stimulating hormone (FSH)?

Stimulates egg maturation in the ovary and sex hormone release Signup and view all the answers

Which part of the pituitary gland secretes hormones directly into the bloodstream?

Posterior pituitary Signup and view all the answers

What distinguishes the posterior pituitary from the anterior pituitary?

It receives hormones from the hypothalamus and stores them Signup and view all the answers

Which of the following is NOT a hormone produced by the anterior pituitary?

Oxytocin Signup and view all the answers

What hormones are transported down the axons of the hypothalamic-hypophyseal tract to the posterior pituitary?

Oxytocin and ADH Signup and view all the answers

Where are oxytocin and ADH stored in the body before release?

Axon terminals in the posterior pituitary Signup and view all the answers

What triggers the release of oxytocin and ADH into the blood?

Action potentials arriving at the axon terminals Signup and view all the answers

Which part of the brain synthesizes GHRH, GHIH, TRH, CRH, GnRH, and PIH?

Hypothalamus Signup and view all the answers

What anatomical structure connects the hypothalamus to the pituitary gland?

Infundibulum Signup and view all the answers

Which of the following accurately describes the posterior lobe of the pituitary?

It stores and releases hormones produced in the hypothalamus. Signup and view all the answers

What is the primary function of the hypothalamic-hypophyseal tract?

To transport hormones to the posterior pituitary Signup and view all the answers

In what context is ADH primarily released?

In response to dehydration Signup and view all the answers

Which of the following non-steroidal anti-inflammatory drugs (NSAIDs) can cause gastrointestinal bleeding and ulcers?

Aspirin Signup and view all the answers

What is the role of corticosteroids in inflammation?

They inhibit phospholipase A2. Signup and view all the answers

What is the primary function of leukotrienes?

To mediate allergic and inflammatory reactions. Signup and view all the answers

Which receptor type does endothelin-1 (ET-1) bind to in smooth muscle tissue to increase blood pressure?

ETA receptors Signup and view all the answers

What effect does the binding of endothelin-1 to ETB receptors have?

Leads to the release of nitric oxide, causing vasodilation. Signup and view all the answers

Which of the following adipokines is primarily associated with energy regulation?

Leptin Signup and view all the answers

How do adipokines function in the body?

They have autocrine, paracrine, and endocrine effects. Signup and view all the answers

What stimulates the formation and release of endothelin-1?

Angiotensin II Signup and view all the answers

What is the primary function of the hormones stored in the posterior pituitary?

Store and release hormones made by the hypothalamus Signup and view all the answers

Which two hormones are primarily associated with the posterior pituitary?

Oxytocin and ADH Signup and view all the answers

What stimulates the release of oxytocin during parturition?

Activation of stretch receptors in the uterus Signup and view all the answers

What effect does antidiuretic hormone (ADH) have on urine production?

Decreases urine production Signup and view all the answers

How does ADH affect blood pressure?

Increases blood pressure by vasopressin action Signup and view all the answers

Which action is primarily caused by oxytocin?

Contraction of uterine smooth muscle Signup and view all the answers

What happens when blood osmotic pressure is low?

ADH secretion is inhibited Signup and view all the answers

What is the role of the thyroid hormone thyroxine?

Regulates metabolism Signup and view all the answers

What physiological effect does parathyroid hormone have?

Stimulates the release of calcium from bones Signup and view all the answers

What triggers the release of ADH in response to high blood osmotic pressure?

Stimulation of hypothalamic osmoreceptors Signup and view all the answers

What role do thyroid follicular cells play in the production of thyroid hormones?

They synthesize thyroglobulin and transport it into the follicle lumen. Signup and view all the answers

Which process is responsible for converting iodide to iodine in the thyroid gland?

Oxidation of iodide in the colloid Signup and view all the answers

What are the products formed by the attachment of iodine to tyrosine in colloid?

Diiodotyrosine (DIT) and monoiodotyrosine (MIT) Signup and view all the answers

How are T3 and T4 formed in the thyroid gland?

By linking iodinated tyrosines together in the lysosome. Signup and view all the answers

What is the first step in the synthesis of thyroid hormones according to the process outlined?

Iodide trapping by thyroid follicular cells Signup and view all the answers

Which of the following substances is actively transported into the thyroid follicular cells for hormone synthesis?

Iodide Signup and view all the answers

What components are necessary to form T4 from iodinated tyrosines?

Iodinated tyrosines and diiodotyrosine Signup and view all the answers

Which element is essential for the formation of thyroid hormones in the synthesis process described?

Iodine Signup and view all the answers

Study Notes

Endocrine Physiology Study Notes

Endocrine system is the internal chemical communication system involving hormones.
Hormones are chemical signals secreted into body fluids (usually blood) and are effective in minute amounts.
Hormones act on cells, tissues, or organs at a location other than where they were produced.
They are not catalysts but rather influence the rate of pre-existing metabolic functions, either positively or negatively.
Hormones are effective at minute concentrations (10⁻¹² to 10⁻⁸ M).
Hormones have a short half-life in circulation (minutes to hours).
Hormones are inactivated or degraded at a constant rate to an inactive form (H*).
Hormone concentration in circulation depends on the secretion rate.
Physiological effects of hormones are proportional to hormone concentration, determined by hormone concentration at the target cell surface, rate of production, rate of delivery, rate of metabolism, degradation, and elimination, sensitivity of target cell, number of functional target cells, and availability of cell membrane receptors on target cells.

Types of Glands

Two different types of glands
- Exocrine - ducted, secrete into ducts
- Endocrine - ductless, secrete into interstitial fluid, diffuse into blood
Endocrine glands include: pituitary, thyroid, parathyroid, adrenal and pineal glands, hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta.

Endocrine Glands and Hormone Function

Hypothalamus: releasing peptide hormone acting on the anterior pituitary (GHRH, CRH, TRH, GnRH)
Anterior Pituitary: Growth Hormone (GH), Corticotrophin (ACTH), Thyroid Stimulating hormone (TSH), Luteinizing hormone (LH), Follicle stimulating hormone (FSH)
Posterior Pituitary: oxytocin, vasopressin (ADH)
Pancreatic Islets of Langerhans: insulin and glucagon
Adrenal cortex: aldosterone and cortisol
Adrenal Medulla: Adrenaline and Noradrenaline
Thyroid Gland: thyroxine and Tri-iodothyronine
Testis: testosterone (androgen)
Ovary and placenta: oestradiol (oestrogens), progesterone

Hormone Classification

Site of Production
Type of action
- Primary hormone of reproduction (FSH, LH, estradiol, progesterone)
- Metabolic hormone (thyroxin, insulin, TSH)
Chemical Structure
- Proteins and polypeptides
- Steroids
- Fatty acids
- Modified amino acid
Size

Hormone Synthesis & Storage

Most endocrine glands produce their hormones continually at levels determined by:
- Body requirements
- Rate of hormone inactivation
- Rate of hormone clearance from the body

Hormone Transport in the Blood

Protein hormones are hydrophilic and carried in the plasma in dissolved form.
Steroids and thyroid hormones are lipophilic and carried in plasma in association with both specific and non-specific binding proteins.
The amount of unbound, active hormone is relatively small.

Hormone-Cell Interaction

Protein hormones have specific receptors on target tissue plasma membranes.
Steroid hormones have specific receptors within the cytoplasm or nucleus.

Post-Receptor Cell Responses

Steroids interact directly with the cell nucleus through complex formation with its cytosolic receptor.
Protein hormones need a messenger because they cannot enter the cell.

Feedback Control Mechanisms

The most important feedback control for hormones is the negative feedback system, where increased hormone concentrations result in decreased production, usually through interaction with the hypothalamus or pituitary gland.
Endocrine secretory patterns influenced by factors like sleep or light, producing circadian rhythms.

Hormone Activity

Hormones affect only specific target tissues with specific receptors.
Receptors are constantly synthesized and broken down.
- Up-regulation: stimulation of receptor synthesis
- Down-regulation: internalization of receptors by endocytosis, receptor synthesis suppression
Circulating hormones circulate in blood throughout the body.
Local hormones act locally:
- Paracrine - act on neighboring cells
- Autocrine - act on the same cell that secreted them

Physiological Effects of Hormones

Action on target cells includes alteration in intracellular protein synthesis, enzyme activity, plasma membrane transport, and secretory activity.
Receptor activation leads to related molecular events inside the cell, including second messenger generation, changes in ion fluxes, activation/inhibition of protein kinases, and activation/inhibition of transcription factors.
These events eventually regulate key metabolic enzyme activity and change the level of key protein gene transcription.

Intracellular Signaling Cascades

Hormone initiates a cascade of reactions involving the signal transfer, signal transformed and relayed, signal amplification, signal diverges, and modulated effects, finally leading to regulation of metabolic pathway and gene expression.

Mechanisms of Hormone Action

Response depends on both hormone and target cell. Lipid-soluble hormones bind to receptors inside target cells, while water-soluble hormones bind to receptors on the plasma membrane, activating a second messenger system.
Responsiveness depends on hormone's concentration, abundance of target cell receptors, and influence exerted by other hormones. Permissive, synergistic, and antagonistic effects may occur.

Receptors

Receptors can be on surface or internal to the target cell.
- Surface receptors are for amino acid-derived hormones
- Internal receptors are for steroid hormones

Feedback Loops (e.g., Hypothalamus-Pituitary-Target Organ)

Some hormones are part of a feedback loop where the increase in a hormone can lead to a decreases or negative feedback.
The response in negative feedback is usually caused by the hormone acting on the hypothalamus or the pituitary gland.
Some processes like ovulation or milk ejection are part of positive feedback, where an increase in a hormone stimulates an increase in another hormone.

Examples of Endocrine Glands and Diseases

Hormone deficiency can result from destruction of the gland due to things like infarction, infection, neoplasms or autoimmune processes, genetic defects in hormone production, or inactivating mutations of hormone receptors.
Hormone excess is due to exogenous intake, overproduction by an endocrine gland, or activating mutations of cell surface receptors.
Gland enlargement can lead to space-occupying lesions, producing pressure effects.

Pituitary Gland and Hormones

The anterior pituitary receives signals from the hypothalamus and releases the appropriate hormones to other glands.
The posterior pituitary stores and releases hormones made by the hypothalamus (oxytocin and ADH)

Hormone Control Mechanisms

Hormone secretion can be regulated by signals from the nervous system, changes in blood chemistry, or other hormones.

Summary of Hormone Effects

All hormones act by regulating the metabolic activities of specific cells.
The magnitude of their effects is proportional to their concentration.

Other Hormone-Producing Structures

Heart
- secretes atrial natriuretic peptide (ANP), which decreases blood Na⁺ concentration, reducing blood pressure and blood volume.
Kidneys
- secrete erythropoietin, stimulating red blood cell production
- secrete renin, initiating the renin-angiotensin-aldosterone mechanism.
Thymus
- secretes thymosin, thymic humoral factor (THF), thymic factor (TF), and thymopoietin, involved in T cell maturation
Pineal gland
- secretes melatonin, a hormone affecting timing of sexual maturation, puberty, and circadian rhythms.
Pancreas -islets of Langerhans are both exocrine and endocrine structures, producing digestive enzymes and regulating blood sugar with the hormones insulin and glucagon.
Gonads -Ovaries secrete estrogens and progesterone; Testes secrete testosterone. They have important roles in reproduction, growth, and development.
Adipose tissue (Adipokines) -Secretes hormones like leptin, adiponectin, and others. These impact various metabolic and physiological functions like regulating energy balance, insulin sensitivity, inflammation and more.

Local Hormones (Autocoids)

These are short-lived hormones produced by almost all body cells, except RBCs, that are often involved in paracrine signaling.
They include various types of chemicals relevant to body functions, including amines (histamine, serotonin), lipid-derived molecules (eicosanoids), and proteins/peptides. Each type is characterized by the particular function.

Specific Examples of Hormones (Action and Effects)

Hormones such as cortisol, ACTH, ghrelin, leptin, PTH etc., have specific actions in their respective systems.

Factors Affecting Hormone Release

Elevated blood glucose, amino acids and fatty acids, parasympathetic nervous system signals, various other hormone levels, and sympathetic nervous system signals. These are factors that influence hormone release in specific glands, like the pancreas or the adrenal glands.

Negative Feedback Regulation

Negative feedback system regulates hormone release, inhibiting further release of the hormone when the concentration reaches a normal level.

Summary Discussion

These are some important details for studying Endocrine Physiology, and are specific examples. The more general overview of the topic has been covered. Further details must be obtained from other sources such as textbooks, research, and relevant literature.

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