Chapter 16-Endocrine System
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What is the endocrine system?
A collection of glands, tissues, and cells that secrete hormones.
What is endocrinology?
The study of the endocrine system, and its diagnosis and treatment of disorders.
What are endocrine glands?
Organs that are sources of hormones.
Which type of gland has ducts?
Exocrine glands.
Which type of gland doesn’t have ducts?
Endocrine glands.
What do exocrine gland ducts do?
They carry secretion to the epithelium surface or the digestive tract.
Where do endocrine glands release hormones?
Directly into the bloodstream through capillary networks.
What are most hormones?
Hydrophilic (water-loving); mixes easily with water.
What hormones are hydrophobic (water-fearing)?
Steriod hormones and thyroid hormones.
What proteins transport hydrophobic hormones in blood?
Albumins and globulins.
What are the two largest mechanisms of communication between cells?
Neurotransmitters and hormones.
Neurotransmitters are?
Released by neurons to travel across the synaptic cleft to the second cell.
How do hormones travel to reach other tissues and organs?
Through the bloodstream.
Which cells can neurotransmitters comminucate with?
Neurons, muscles, and glands.
What are target organs or target cells?
Organs or cells that have receptors for a hormone and can respond to it.
What must a cell have to respond to a particular hormone?
The correct receptor for that hormone.
Which system reacts faster: nervous or endocrine?
Nervous system.
Which system has effects that can last for days or longer?
Endocrine system.
Which system adapts quickly to long-term stimuli?
Nervous system.
Which system’s responses persist and adapt slowly?
Endocrine system.
Which system has targeted and specific effects?
Nervous system.
Which system has general, widespread effects on many organs?
Endocrine system.
What three chemicals can function as both hormones and neurotransmitters?
Norepinephrine, dopamine, and ADH
What do norepinephrine and glucagon cause in the liver?
Glycogen hydrolysis.
What is glycogen hydrolysis?
The breakdown of stored glycogen.
How do the nervous and endocrine system regulate each other?
Neurotransmitters affect glands and hormones affect neurons.
What are neuroendocrine cells?
Cells that share characteristics of both nervous and endocrine systems.
Where are neuroendocrine cells found?
Hypothalamus.
What are the variations to hormonal secretion?
Daily (circadian) secretion, monthly secretion, neural, hormonal, and humoral stimuli.
What are the three stimuli for hormone secretion?
Neural, hormonal, and humoral stimuli.
What is neural stimuli and what triggers it?
Quick-immediate stimuli that is triggered by nerve signals.
What is hormonal stimuli and what triggers it?
Slower and longer lasting stimuli that is triggered by other hormones.
What triggers humoral stimuli?
Changes in blood or interstitial fluid.
What are synergistic effects?
When multiple hormones work together
Example: FSH and testosterone working together to promote sperm production.
What are permissive effects?
When one hormone enhances a target organ’s response to another hormone.
Ex: Estrogen preparing the uterus for the action of progesterone.
What are antagonistic effects?
When one hormone opposes the action of another.
Ex: Insulin lowers blood glucose and glucagon raises blood gucose.
What determines whether a cell can respond to a hormone?
It must have that specific receptor for that hormone.
What are hormone receptors made of?
Proteins or glycoprotiens.
Where can hormone receptors be found?
Plasma membrane, cytoplasm, or nucleus.
What happens when a hormone binds to its receptors?
It activates the receptor, which turns on the metabolic pathways in the target cell.
What is signal amplification (cascade effect)?
When one hormone triggers the production of many enzyme molecules.
Why are hormones considered potent?
A small amount can produce a large effect.
What is up-regulation?
Increasing the number of receptors, making a cell more sensitive to a hormone.
What is down-regulation?
Decreasing the number of receptors, making a cell less sensitive to a hormone.
What is the hypothalamus?
A flattened funnel shape that forms the floor and walls of the third ventricle.
What does the hypothalamus do?
It regulates important body functions carried out by the pituitary gland including water balance, temperature regulation, sex drive, and childbirth.
What is the pituitary gland (Hypophysis)?
An endocrine gland connected to the hypothalamus by the infundibulum.
Where is the pituitary gland located?
In the sella turcica of the sphenoid bone.
What is the anterior pituitary gland and what does it do?
The front portion of the pituitary gland that produces and releases its own hormones.
What is the posterior pituitary gland and what does it do?
The back portion of the pituitary gland that stores and releases hormones produced by the hypothalamus.
What is negative feedback?
A process where increased hormone levels signal the body to decrease hormone levels.
What is the purpose of the negative feedback loop?
To maintain homeostasis (balance)
What is an example of negative feedback?
High thyroid hormone levels inhibit TRH and TSH release.
What is positive feedback?
A process where a response causes even more hormone release.
What is an example of positive feedback?
During childbirth, uterine stretching triggers oxytocin release, causing stronger contractions.
Where is the pineal gland located?
In the brain, attatched to the roof of the third ventricle.
What hormone does the pineal gland produce?
Melatonin.
What is the function of melatonin?
Regulates circadian rhythms (sleep-wake cycle) and promotes sleep.
When is melatonin primarily released?
At night, especially in darkness.
What can influence melatonin production?
Light exposure and seasonal changes.
Where is the thymus gland located?
At the mediastinum, above the heart.
What hormone does the thyroid gland produce?
Thymosin.
What is the primary function of thymosin?
Promote the development and maturation of T lymphocyctes (T cells).
What is the role of T lymphocytes?
Help defend the body against infections.
What happens to the thymus gland after puberty?
It gradually shrinks.
Where is the thyroid gland located?
Below the larynx, next to the trachea.
What are the two lobes of the thyroid gland connected by?
The isthmus.
What are the two main types of hormone-secreting cells in the thyroid.
Follicular cells and parafollicar (C) cells.
What hormones do follicular cells produce?
T3 (triiodothyronine) and T4 (thryoxine).
What hormones do parafollicular (C) cells produce?
Calcitonin.
What nutrient is necessary for thyroid hormone production?
Lodine.