Endocrine Flashcards
What is a hormone?
A hormone is a chemical messenger manufactured by endocrine glands that has been released into the bloodstream
Define the endocrine system
The endocrine system is a collection of glands around the body responsible for
- manufacturing
- storing, and
- releasing
hormones into the blood stream, so that it can be transported to target cells (have hormone specific receptors) distant from the source.
What functions do hormones control?
What kind of action are their effects concerned with?
Why must blood hormone levels be closely regulated within the ‘normal range’?
Hormones regulate:
- metabolism
- growth
- reproductive function
- body’s stress response
Hormones control processes that require duration of action (length), rather than speed of action, which is provided by the nervous system
Blood hormone levels must be controlled (within ‘normal range’) for homeostasis “standing still”
Why is homeostasis of “normal physiological ranges” necessary?
How do hormones maintain homeostasis?
Normal physiological conditions are necessary for normal cellular function: or else our organs and tissues stop working properly.
The activity of hormones (maintenance of homeostasis) is almost always controlled by negative feedback mechanisms. (i.e. if the body goes one way, the hormones take it back a notch the other way)
What are the different types of hormonal signalling?
Endocrine
- Cell is released into the blood stream and transports to cells distant from the source.
Paracrine
- Chemical signal acts on neighboring cells
Autocrine
- Chemical sign acts on the cell that released it.
What are the different types of hormonal secretion patterns?
Diurnal secretion pattern
- Predictable over a 24 hour period
Constant secretion pattern
- Maintenance of physiology function at all times
Episodic secretion pattern
- Reacts to a specific stimulus and less predictable
What are the different types of tumours and clinical hormonal problems they can cause?
A tumour on an endocrine gland can cause an inappropriate magnitude of change in hormonal (cellular) activity
- Functioning tumour: too much hormone secreted (hypersecretion)
- Non-functioning tumour: destroys endocrine gland and too little hormone secreted (hyposecretion)
Label the regions of the body and their associated endocrine glands
Where is the hypothalamus located?
What is the significance of this location?
The hypothalamus is located in the Diencephalon, under the thalamus (the diencephalon consists of the thalamus + hypothalamus).
The diencephalon forms the central core of the cerebrum, which has connections to the right and left cerebral hemispheres and the midbrain (the top part of the brainstem)
This is significant because the brainstem is the part of the brain that is continuouswith the spinal cord, and controls the flow of messages between the brain and the rest of the body.
Label the diagram
What is the function of the hypothalamus?
Hypothalamic neurons secrete either:
1. Releasing hormones
- stimulatethe anterior pituitary to release its hormone(s) into the bloodstream
2. Release-inhibitory hormones
- prevent the anterior pituitary releasing hormone(s) into the bloodstream
Describe the location and surface anatomy of the pituitary gland
The pituitary gland hangs from the hypothalamus. It sits in the hypophyseal fossa of the sphenoid bone (a saddle-shaped depression in the body of the sphenoid bone of the human skull).
It is anatomically and functionally divided into a posterior lobe (also called neurohypophysis) and an anterior lobe.
- The posterior lobe is a continuation of the hypothalamus via the infundibulum (funnel)
- Axons project down from the hypothalamus through the infundibulum to the posterior lobe
- The anterior lobe doesn’t connect to the hypothalamus but rather wraps around the posterior lobe.
What is the pituitary gland referred to? Why?
‘Master Gland’ – Hormones secreted from the pituitary control output of many other endocrine glands
Label the diagram
What is the function of the posterior pituitary gland?
Manufactures two hormones:
Oxytocin
- Ejection of breast milk
- Stimulates uterine contraction in childbirth
- Social bonding (so that you like your child – evolutionary response)
Vasopressin (ADH or antidiuretic hormone)
- Aids water retention (works in conjunction with kidney)
List the hormones secreted by the anterior pituitary gland
- Growth hormone (GH)
- Prolactin (milk production)
- Thyroid stimulating hormone (TSH)
- Adrenocorticotrophic hormone (ACTH)
- Lutenising hormone (LH)
- Follicle stimulating hormone (FSH
2-step process for the anterior pituitary gland secretion:
Dependant upon the hypothalamus secreting release hormones or release-inhibiting hormones, the anterior pituitary gland then acts.
What is a portal system?
How many are there in the body?
List the name and components of the endocrine gland portal system
A portal system is two venous capillary beds joined by a portal vein.
There are 2 in the body:
- Hepatic Portal System (GI tract: liver)
2. Hypophyseal Portal System (Endocrine System)
- 1st capillary bed in hypothalamus/infundibulum
- Hypophyseal portal veins transport hormones produed in hypothalamus via infundibulum
- 2nd capillary bed in anterior pituitary gland
- Hypophyseal veins carry blood to SVC
Describe the anatomy of the thyroid gland
The thyroid gland is an endocrine gland, divided into two lobes which are connected by an isthmus. It is said to have a butterfly shape.
It is located in the anterior and inferior neck, spanning between the C5 and T1 vertebrae.
It wraps around the cricoid cartilage and superior tracheal rings. It is inferior to the thyroid cartilage of the larynx.
Label the diagram
What are the hormones produced by the thyroid gland (and what does it use to produce them)?
What are their functions?
The thyroid gland uses iodine to manufacture the 2 hormones:
- triiodothyronine (T3)
- thyroxine(T4)
Thyroid hormones regulate metabolism & stimulate growth
We cannot live without T3!!
How many parathyroid glands do we have? Where do they lie?
4 (2 on each side)
They lie on the back of the lobes of the thyroid gland
Label the diagram (including the central gray areas)
What hormone does the parathyroid gland produce?
What is the function of the hormone? Why is it important?
What is unique about the hormone?
- Manufacture & secrete parathyroid hormone (PTH)
- PTH controls the amount of calcium in blood and bone
- Normal muscle & nerve function depends on blood Ca++ levels being in the normal range
- PTH is NOT under pituitary control (the glands monitor blood Ca++and respond directly)
Describe the blood supply (arterial and venous) of the thyroid and parathyroid glands
Thyroid arteries:
- Right and left superior thyroid arteries branch from the right and left common carotid arteries
- Right and left inferior thyroid arteries branch from right and left subclavian arteries
- Thyroid ima artery: a variant. Varies as to where it branches off from (could be braciocephalic trunk, the arch of the aorta, the right common carotid artery or even the subclavian vein). If it is centrally over the trachea, a tracheotomy should not be made in the center as it will cut the artery
Thyroid veins:
- Right and left super thyroid vein drains into right and left internal jugular vein
- Right and left middle thyroid vein drains into right and left internal jugular vein
- Right and left inferior thyroid vein both drain into LEFT braciocephalic vein
