Anatomy Lecture 4: The Endocrine System

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Questions and Answers

What hormone is secreted by alpha or A cells in the pancreatic islets?

Insulin

Pancreatic polypeptide

Somatostatin

Glucagon (correct)

Which hormone is responsible for lowering blood sugar levels?

Testosterone

Insulin (correct)

Somatostatin

Glucagon

What is the function of somatostatin secreted by delta or D cells?

Stimulates insulin secretion

Stimulates glucagon secretion

Promotes glucose absorption

Inhibits both insulin and glucagon (correct)

What is produced by the F cells in the pancreatic islets?

Pancreatic polypeptide Signup and view all the answers

What is the primary action of glucagon on hepatocytes?

Convert glycogen into glucose Signup and view all the answers

Which hormone is primarily involved in regulating the menstrual cycle and maintaining pregnancy?

Progesterone Signup and view all the answers

What effect does high blood glucose (hyperglycemia) have on glucagon release?

Inhibits glucagon release Signup and view all the answers

Which of the following hormones does not inhibit FSH production?

Relaxin Signup and view all the answers

What distinguishes the endocrine system from the nervous system?

It releases hormones that have a broader influence. Signup and view all the answers

Which of the following glands is NOT classified as an endocrine gland?

Salivary gland Signup and view all the answers

What term describes hormones that act on neighboring cells?

Paracrine hormones Signup and view all the answers

How do hormones specifically affect their target tissues?

Through specific receptors present on target tissues. Signup and view all the answers

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

It secretes hormones that regulate other endocrine glands. Signup and view all the answers

What is the term for the process by which hormone receptors are reduced in number?

Down-regulation Signup and view all the answers

Which of the following is a type of local hormone that acts on the same cell that secreted it?

NO (Nitric Oxide) Signup and view all the answers

Which statement regarding exocrine and endocrine glands is true?

Endocrine glands are ductless and release hormones into interstitial fluid. Signup and view all the answers

Where is the pineal gland located?

Attached to the roof of the 3rd ventricle of the brain Signup and view all the answers

What hormone is derived from serotonin?

Melatonin Signup and view all the answers

During which condition is more melatonin produced?

During darkness Signup and view all the answers

What does the thymus produce that is involved in T cell maturation?

Thymosin Signup and view all the answers

What term describes helpful stress?

Eustress Signup and view all the answers

What is the first stage of the general adaptation syndrome (GAS)?

Flight-or-fight Signup and view all the answers

Prolonged exposure to cortisol can lead to which of the following?

Wasting of muscles Signup and view all the answers

What is one possible effect of stress on the gastrointestinal tract?

Ulceration Signup and view all the answers

What type of hormones typically use transport proteins to circulate in the bloodstream?

Lipid-soluble hormones Signup and view all the answers

Lipid-soluble hormones bind to which part of the target cell?

Receptors inside the cell Signup and view all the answers

Which of the following is NOT a type of water-soluble hormone?

Steroid hormones Signup and view all the answers

What is the main role of second messengers in water-soluble hormone action?

To amplify the hormone signal Signup and view all the answers

Which factor does NOT affect the responsiveness of a target cell to a hormone?

The time of day Signup and view all the answers

What mechanism is primarily responsible for hormonal regulation in the body?

Negative feedback primarily Signup and view all the answers

What is the function of adenylate cyclase in water-soluble hormone signaling?

To convert ATP to cAMP Signup and view all the answers

Which of the following is a characteristic of eicosanoid hormones?

They are water-soluble and derived from fatty acids Signup and view all the answers

What happens when a lipid-soluble hormone binds to its receptor?

Gene expression is altered Signup and view all the answers

What is a primary example of a hormone exerting a permissive effect?

One hormone enhancing the effect of another Signup and view all the answers

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

It acts as a major link between the nervous and endocrine systems. Signup and view all the answers

Which type of hormones does the anterior pituitary primarily release?

Tropic hormones that act on other endocrine systems. Signup and view all the answers

What role does the hypothalamic-hypophyseal portal system play in hormone regulation?

Transports hypothalamic hormones to the anterior pituitary. Signup and view all the answers

Which of the following hormones is secreted by the anterior pituitary and stimulates growth?

Human growth hormone (hGH). Signup and view all the answers

What does follicle-stimulating hormone (FSH) stimulate in the ovaries and testes?

Oocyte development in the ovaries and testosterone production in the testes. Signup and view all the answers

Which hormone is primarily responsible for promoting milk secretion?

Prolactin (PRL). Signup and view all the answers

What is the physiological role of adrenocorticotropic hormone (ACTH)?

Stimulates glucocorticoid secretion by the adrenal cortex. Signup and view all the answers

Which hormone's role in humans is still unknown?

Melanocyte-stimulating hormone (MSH). Signup and view all the answers

Study Notes

Endocrine and Nervous Systems

The endocrine and nervous systems work in tandem to regulate body functions.
The nervous system operates through nerve impulses and neurotransmitters, providing fast responses with brief effects on specific targets.
The endocrine system utilizes hormones, which are released in one area but influence cells elsewhere, resulting in slower but longer-lasting effects.

Endocrine Glands

Glands are categorized into exocrine (ducted) and endocrine (ductless).
Endocrine glands secrete hormones directly into the interstitial fluid for diffusion into the bloodstream.
Major endocrine glands include the pituitary, thyroid, parathyroid, adrenal, and pineal glands, alongside other organs like the hypothalamus, pancreas, and ovaries, among others.

Hormone Activity

Hormones target specific tissues through specialized receptors, which are actively synthesized and degraded.
Receptor regulation includes down-regulation, up-regulation, and the blocking of hormone receptors, exemplified by the drug RU486 (Mifepristone).

Types of Hormones

Circulating hormones: Travel throughout the body via the bloodstream.
Local hormones: Act in the vicinity of secretion, classified as:
- Paracrine hormones: Influence neighboring cells (e.g., IL-2).
- Autocrine hormones: Affect the secreting cell itself (e.g., NO).

Chemical Classes of Hormones

Lipid-soluble hormones: Require transport proteins and include:
- Steroids derived primarily from cholesterol.
- Thyroid hormones (T3 and T4) linked to iodine.
- Nitric oxide (NO), functioning as both neurotransmitter and hormone.
Water-soluble hormones: Function in free form and encompass:
- Amines.
- Peptides/proteins.
- Eicosanoids.

Mechanisms of Hormone Action

Hormonal responses vary based on the hormone and receptor type.
Lipid-soluble hormones interact with intracellular receptors, while water-soluble hormones bind to plasma membrane receptors, activating secondary messenger systems.
Target cell responsiveness is influenced by hormone concentration, receptor abundance, and other hormonal interactions (permissive, synergistic, or antagonistic).

Hormonal Regulation and Feedback

Hormone secretion is governed by:
- Nervous system signals.
- Blood chemical changes.
- Other hormones.
Most hormone regulation occurs through negative feedback, with few exceptions for positive feedback.

Hypothalamus and Pituitary Gland

The hypothalamus connects the endocrine and nervous systems.
The pituitary gland, linked to the hypothalamus via infundibulum, consists of anterior and posterior sections.
The anterior pituitary releases hormones regulated by hypothalamic releasing and inhibiting hormones, often classified as tropic hormones that influence other endocrine glands.

Anterior Pituitary Hormones

Human Growth Hormone (hGH): Stimulates insulin-like growth factors (IGFs) for growth and protein synthesis.
Thyroid-Stimulating Hormone (TSH): Promotes thyroid hormone production.
Follicle-Stimulating Hormone (FSH): Supports ovarian and testicular functions.
Luteinizing Hormone (LH): Triggers ovulation and testosterone production.
Prolactin (PRL): Promotes milk secretion from mammary glands.
Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex glucocorticoid secretion.
Melanocyte-Stimulating Hormone (MSH): Role in humans remains unclear.

Pancreatic Islets

The pancreas functions as both an exocrine and endocrine gland, with 99% of its cells producing digestive enzymes.
Pancreatic islets (Langerhans) contain:
- Alpha cells: Secrete glucagon to raise blood sugar levels.
- Beta cells: Release insulin to lower blood sugar levels.
- Delta cells: Produce somatostatin to inhibit glucagon and insulin.
- F cells: Secrete pancreatic polypeptide to inhibit several digestive functions.

Ovaries and Testes

Gonads produce gametes and hormones.
Ovaries generate estrogen and progesterone, crucial for reproductive functions, and inhibin to regulate FSH.
Testes produce testosterone, regulating sperm production and male characteristics, also inhibiting FSH.

Pineal Gland

Located at the midline of the brain’s third ventricle, it contains pinealocytes that secrete melatonin.
Melatonin plays a role in regulating circadian rhythms, with production increasing in darkness.

Thymus and Endocrine Functions

The thymus, behind the sternum, is vital for T cell maturation.
It produces thymosin, thymic humoral factor (THF), thymic factor (TF), and thymopoietin.

Stress Response

Eustress is beneficial, while distress is harmful.
The body activates a general adaptation syndrome (GAS) in response to stress, comprising:
- Initial fight-or-flight reaction.
- Slower resistance phase.
- Potential exhaustion from prolonged cortisol exposure, affecting muscle, immune, GI, and pancreatic functions.

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Description

Explore the functions of the endocrine system in this lecture. Understand how it interacts with the nervous system to coordinate body functions through hormones and nerve impulses. This quiz focuses on the mechanisms of hormonal regulation and the contrasting speed of responses between these two systems.