Endocrine System Overview

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Questions and Answers

Which hormone is responsible for stimulating the secretion of cortisol from the adrenal cortex?

Thyroid-stimulating hormone (TSH)

Adrenocorticotropic hormone (ACTH) (correct)

Luteinizing hormone (LH)

Follicle-stimulating hormone (FSH)

What is the role of growth hormone-releasing hormone (GHRH) in the endocrine system?

Promotes thyroid hormone secretion

Inhibits the action of ghrelin

Stimulates the release of somatostatin

Stimulates the secretion of growth hormone (correct)

What is the effect of prolactin on the body?

Enhances breast development and milk production (correct)

Promotes the vascularisation of the thyroid gland

Stimulates cortisol release

Regulates testosterone secretion

Which hormone directly stimulates the growth and development of ovarian follicles?

Follicle-stimulating hormone (FSH) Signup and view all the answers

What inhibits the secretion of prolactin from the anterior pituitary?

Dopamine (DA) Signup and view all the answers

Which hormone stimulates the secretion of thyroid hormones from the thyroid gland?

Thyroid-stimulating hormone (TSH) Signup and view all the answers

How does luteinizing hormone (LH) affect males?

Stimulates secretion of testosterone Signup and view all the answers

Which of the following hormones is secreted in response to corticotropin-releasing hormone (CRH)?

Adrenocorticotropic hormone (ACTH) Signup and view all the answers

What effect does thyroid hormone have on metabolic rate?

Increases overall basal metabolic rate Signup and view all the answers

What is the primary function of the hypothalamus in the endocrine system?

To integrate signals and convert them into chemical messages Signup and view all the answers

What type of hormones is secreted by the adrenal cortex?

Mineralocorticoids Signup and view all the answers

Which hormone is considered stimulatory to the anterior pituitary?

Thyrotropin-releasing hormone (TRH) Signup and view all the answers

Which layer of the adrenal cortex is responsible for secreting aldosterone?

Zona glomerulosa Signup and view all the answers

What is the main function of vasopressin in the body?

Regulates urinary water loss and balance Signup and view all the answers

How does the hypothalamus influence the anterior pituitary gland?

By releasing hormones that directly stimulate it Signup and view all the answers

Which hormone is primarily responsible for stimulating milk ejection during breastfeeding?

Oxytocin Signup and view all the answers

Which hormones are secreted by the adrenal medulla?

Catecholamines Signup and view all the answers

How does thyroid hormone affect sympathetic nervous system activity?

Increases heart rate and myocardial contractility Signup and view all the answers

What triggers the production of melatonin in the pineal gland?

Darkness and the suprachiasmatic nucleus Signup and view all the answers

What type of hormones does the anterior pituitary release into systemic circulation?

Tropic hormones Signup and view all the answers

What role do inhibitory hormones play in the hypothalamic function?

They prevent the release of certain hormones from the anterior pituitary Signup and view all the answers

What is the role of glucocorticoids secreted by the adrenal cortex?

Control metabolism and stress adaptation Signup and view all the answers

Which gland is associated with the secretion of T3 and T4 hormones?

Thyroid gland Signup and view all the answers

Which of the following is NOT a function of melatonin?

Regulates plasma volume Signup and view all the answers

Which of the following is a neuroendocrine transducer?

The hypothalamus Signup and view all the answers

Which statement describes the effect of thyroid hormone on intermediary metabolism?

Biphasic effects on carbohydrate, fat, and protein metabolism Signup and view all the answers

What is the function of gonadotropin-releasing hormone (GnRH)?

To stimulate the release of tropic hormones from the anterior pituitary Signup and view all the answers

What is the role of the parafollicular or C cells in the thyroid gland?

Secret calcitonin Signup and view all the answers

What is the primary effect of the adrenal cortex's zona reticularis?

Production of sex hormones Signup and view all the answers

What factor primarily stimulates oxytocin secretion?

Uterine contractions during labor Signup and view all the answers

Which hormone serves as a Growth hormone-inhibiting hormone (GHIH)?

Dopamine Signup and view all the answers

What physical characteristic describes the pineal gland?

Tiny and pinecone-shaped Signup and view all the answers

What substance is testosterone converted into in target tissues?

Dihydrotestosterone (DHT) Signup and view all the answers

Which of the following is NOT a key function of testosterone?

Mediates cardio-protective effects Signup and view all the answers

What role do oestrogens play in the female body?

Promote maturation of reproductive organs Signup and view all the answers

During which phase does progesterone production increase markedly?

Luteal phase Signup and view all the answers

Which of the following is a function of progesterone?

Helps mediate sexual response in the brain Signup and view all the answers

What happens to testosterone production during puberty?

Increases rapidly Signup and view all the answers

What effect do oestrogens have on bone density?

Increase bone density Signup and view all the answers

Which hormone is referred to as the 'hormone of pregnancy'?

Progesterone Signup and view all the answers

What is a primary function of the endocrine system?

To secrete hormones that regulate various bodily functions Signup and view all the answers

Which of the following accurately describes how hormones function within the endocrine system?

Hormones are carried in the bloodstream to interact with distant target cells. Signup and view all the answers

Which division of the endocrine system includes the glands located throughout the body?

Peripheral endocrine glands Signup and view all the answers

What would occur as a result of over-secretion of a hormone?

Enhanced physiological responses Signup and view all the answers

The major function of the central endocrine glands primarily involves:

Secreting hormones that affect distant targets Signup and view all the answers

Which of the following statements about endocrine signaling is correct?

Hormones are released into the bloodstream to regulate distant target cells. Signup and view all the answers

Which of the following best describes 'neurosecretory cells' in the context of the endocrine system?

Neurons that release hormones into the bloodstream. Signup and view all the answers

Which outcome is expected from under-secretion of a major hormone?

Reduced metabolic activity in target cells Signup and view all the answers

Study Notes

Endocrine System 1

The endocrine system is one of the body's major regulatory systems.
It regulates, integrates, coordinates, and controls important cellular, organ, and body functions, including cellular metabolism, water and electrolyte balance, cell growth, development, and reproduction.
It also helps the body cope with stressful situations and controls the circulatory and digestive systems.
The endocrine system consists of specialized ductless glands and neurosecretory cells scattered throughout the body.
These glands and cells secrete biologically active chemical messengers called hormones into the bloodstream.
Hormones are transported in the bloodstream to interact with distant target cells.
This interaction leads to a specific response in terms of metabolism, growth, or reproduction.

Outline of Lecture

General principles of endocrine function
Types of hormones and signaling pathways or mechanisms
Broad divisions of the endocrine system
The central endocrine glands and their hormones
The peripheral endocrine glands and their hormones

Learning Outcomes

Describe the basic principles of endocrine signaling.
Describe the major divisions of the endocrine system.
Give a detailed account of the major hormones of the central endocrine glands and their actions.
Give a detailed account of the major hormones of the peripheral endocrine glands and their actions.
Predict the consequences of over or under-secretion of major hormones.

General Principles of Endocrine Function

The endocrine system consists of ductless glands and neurosecretory cells.
These glands and cells release hormones into the bloodstream for interaction with target cells.
This interaction leads to specific metabolic, growth, or reproduction responses in the target cells.

Chemical Classification of Hormones

Amines and amino acid derivatives (e.g., norepinephrine, epinephrine, melatonin, thyroid hormones)
Polypeptides and proteins (e.g., TRH, ADH, GH, FSH, insulin)
Steroids (e.g., cortisol, testosterone, estradiol, progesterone)

Synthesis & Transport of Hormones

Vesicle-mediated pathway:
- Hormones like peptides and proteins are synthesized in the rough endoplasmic reticulum (rER) and packaged in vesicles for secretion.
Non-vesicle-mediated pathway:
- Hormones like steroids are synthesized in the smooth endoplasmic reticulum (sER) and released directly into the bloodstream.
Transport:
- Peptide and amine hormones circulate freely in the blood.
- Steroid and thyroid hormones bind to carrier proteins for transport.

Control of Hormonal Secretion

Pulsatile or cyclical secretion: Hormones are released in bursts over time.
Diurnal or circadian rhythm: Hormones are released in a daily pattern.
Negative feedback control: The product of a hormonal pathway inhibits further hormone release to maintain homeostasis.

Hormonal Signaling

Hormones interact with specific receptors on target cells to produce their effects.
Two types of hormonal receptors:
- Cell surface receptors:
  - Receptor-ion channels, G-protein-coupled receptors, and tyrosine kinase-linked receptors.
- Intracellular/nuclear receptors: Steroid and thyroid hormones bind intracellular or nuclear receptors.

Endocrine Disorders

Hyposecretion: Endocrine gland secretes too little of its hormones, which may be primary, secondary, or tertiary in nature.
Hypersecretion: Endocrine gland secretes too much of its hormones, which may be primary, secondary, or tertiary in nature.
Abnormal Target Cell Responsiveness: Issues with receptor down-regulation or receptor upregulation.

The Central Endocrine Glands

Hypothalamus, Pituitary Gland, Pineal Gland

The Peripheral Endocrine Glands

Thyroid glands, Adrenal glands, Endocrine pancreas, Parathyroid glands, The Gonads (ovaries & testes)

The Hypothalamus & Pituitary Gland

Located in the diencephalon
Function Cooperatively as master regulators of the endocrine system
Connected by blood flow via the hypophyseal portal system (to the anterior pituitary)
Connected by the hypothalamo-hypophyseal nerve tract (to the posterior pituitary)
Hypothalamus is the coordinating center for endocrine, behavioral & autonomic nervous system function.
Hypothalamus receives & integrates various brain signals, converts electrical to chemical messages, and controls pituitary hormone secretion.
Pituitary has two lobes (anterior and posterior).
- Anterior pituitary comprises several cell types secreting various hormones.
- Posterior pituitary stores and releases hypothalamic hormones, such as ADH & Oxytocin

Hypothalamic Hormones

Stimulatory (e.g., GHRH, TRH, CRH, GnRH).
Inhibitory (e.g., Somatostatin, Dopamine).

The Pituitary Gland

Consists of two lobes
- Anterior pituitary (Adenohypophysis): Secretes six major hormones
- Posterior pituitary (Neurohypophysis): Stores and releases two major hormones (ADH & Oxytocin)

Anterior Pituitary Hormones

Growth Hormone (GH), Thyroid-stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), Follicle-stimulating Hormone (FSH), Luteinizing Hormone (LH), Prolactin (PRL)

Posterior Pituitary Hormones

Vasopressin (ADH).
Oxytocin.

The Pineal Gland

Tiny, cone-shaped gland in the diencephalon.
Secretes melatonin, the 'hormone of darkness'.
Production stimulated by the suprachiasmatic nucleus (SCN), the body's biological clock.
Synchronizes circadian rhythms with the day/night cycle.
Promotes sleep.
Influences reproductive activity (onset of puberty).

The Thyroid Gland

Located in the neck, below the larynx.
Two lobes connected by an isthmus.
Consists of two types of secretory cells (follicular & parafollicular/C).
Follicular cells secrete the iodine-containing hormones T3 & T4.
Parafollicular cells secrete calcitonin (a peptide hormone).

Thyroid Hormone

Formed from iodine and tyrosine.
Synthesized as thyroglobulin (TG) in the follicular cells.
Thyroglobulin is moved into the colloid.
Iodide is taken up and attached to tyrosine in thyroglobulin to form MIT and DIT.
MIT and DIT couple to make T3 and T4, which remain attached to thyroglobulin until release.
Release is stimulated by TSH, involving endocytosis, proteolysis, and diffusion of T3 & T4 into the blood.
T4 is converted to T3 in liver and kidneys.

Functions of Thyroid Hormone

Normal growth and CNS development.
Effects on metabolism (basal metabolic rate, heat production, intermediary metabolism, sympathetic activity).

The Adrenal Glands

Paired organs above the kidneys
Divided into two regions: cortex and medulla
Cortex
- Zona glomerulosa: secretes mineralocorticoids (aldosterone) regulating Na+/K+ balance and blood pressure.
- Zona fasciculata: secretes glucocorticoids (cortisol) regulating carbohydrate, protein, and fat metabolism, and stress response.
- Zona reticularis: secretes sex hormones (like DHEA), supplementing gonadal hormones.
Medulla
- Secretes catecholamines (epinephrine and norepinephrine) promoting "fight or flight" responses.

The Endocrine Pancreas

Composed of clusters of cells called islets of Langerhans.
Three main cell types: alpha cells (secrete glucagon), beta cells (secrete insulin), and delta cells (secrete somatostatin).
Secretions are regulated by blood glucose levels.

Pancreas Hormones: Insulin

Important anabolic hormone regulating fuel metabolism.
Promotes glucose, fatty acid, and amino acid uptake and storage.
Enhances their conversion to glycogen, triglycerides, and proteins.

Pancreas Hormones: Glucagon

Opposes the action of insulin.
Mobilizes energy-rich molecules from storage sites to increase blood glucose levels.
Stimulates glycogenolysis & gluconeogenesis for hepatic glucose release, lipolysis & ketogenesis.

Hormones Involved in Calcium Homeostasis

Parathyroid hormone (PTH): Raises blood calcium levels by increasing bone resorption, renal calcium reabsorption, and activating vitamin D.
Vitamin D: Increases intestinal calcium absorption.
Calcitonin: Lowers blood calcium levels by decreasing bone resorption and renal calcium reabsorption.

The Gonads

Testes in males and ovaries in females.
Primary functions:
- Testes: sperm production and secretion of testosterone.
- Ovaries: egg cell production and secretion of estrogen/progestins.

The Male Sex Hormones (Androgens)

Testosterone: Secreted by Leydig cells in the testes
- Converted to DHT in target tissues.
- Promotes development and maintenance of male reproductive organs
- Promotes male secondary sexual characteristics, like facial hair and deeper voice.
- Maintains sexual drive, increases bone thickness and strength, increases basal metabolic rate & muscle mass.

The Female Sex Hormones

Estrogens (estradiol):
- Secreted by granulosa cells in the ovaries.
- Promotes maturation/maintenance of the reproductive organs
- Promotes secondary sexual characteristics, like breasts and fat distribution.
- Plays a role in menstruation, pregnancy, and childbirth.
- Reduces bone resorption and increases bone density.
Progestins (progesterone):
- Secreted by granulosa & theca cells in the ovaries.
- Production increases during the luteal phase. Also known as the "hormone of pregnancy."
- Plays critical role in the female reproductive cycle, mediating sexual response, preparing the uterus for implantation, and rendering the cervical canal impenetrable to sperm post-implantation.
- Inhibits uterine contractions and Na+-retaining activity of aldosterone promoting natriuresis.

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Description

Test your knowledge on the human endocrine system with this quiz covering key hormones, their functions, and their interactions. From cortisol secretion to the roles of GHRH and prolactin, this quiz provides a comprehensive overview of essential topics in endocrinology.