Chapter 2: Chemical Messengers Flashcards
What is an exocrine gland?
Glands that secrete into a duct that carries the secretion to the surface of the body or to one of the body cavities.
What are some examples of exocrine glands?
- sweat glands
- salivary glands
- mucous glands
What are endocrine glands?
Glands that secrete hormones into the extracellular fluid that surrounds the cells that make up the gland. The secretion usually then passes into the capillaries to be transported by the blood.
What are some examples of endocrine glands?
- pituitary
- thymus
- thyroid
What is a hormone?
The secretion of an endocrine gland
What is a target cell?
A cell whose activity in affected by a particular hormone.
What is a target organ?
An organ whose activity is affected by a particular hormone.
What is a paracrine?
Any chemical secreted by a cell that diffuses to and affects adjacent cells, also called a local hormone
What are the characteristics of protein and amine hormones?
- water soluble
- receptor outside and secondary messenger
How do protein and amine hormones work?
- Hormone attaches to the corresponding receptor protein in the membrane of the target cell.
- This combination causes a secondary messenger substance to diffuse through the cell and activate particular enzymes.
What are the characteristics of steroid hormones?
- lipid soluble
- crosses membrane, attaches to receptor inside
What is enzyme amplification?
The process in which one hormone molecule causes the manufacture or activation of thousands of enzymes
What occurs once the hormone has produced the required effect?
It must be turned off. The hormone molecules are broken down in the target cells, or mostly liver and kidneys and are then excreted in bile or urine.
What is a negative feedback system?
Where the response produced by the hormone is opposite of the stimulus that caused the secretion.
What are releasing factors?
Hormones secreted by the hypothalamus that stimulate the release of a hormone
What are inhibiting factors?
Hormones released by the hypothalamus that slow down the release of a hormone.
Why is the pituitary gland known as the master gland?
Because many pituitary hormones regulate the activity of other endocrine glands
The Pineal Gland
Location: deep inside the brain
Hormone: melatonin
Target: all cells
Function: regulates sleep patterns
The Thyroid Gland
Location: in the neck below the larynx
Hormone: thyroxin
Target: most cells
Function: increases metabolic rate and therefore oxygen consumption and heat production
The Parathyroid Gland
Location: usually 4, embedded in the rear surface of the thyroid
Hormone: parathyroid hormone (PTH)
Target: kidneys, bones, intestines
Function: controls calcium and phosphate levels in the blood
The Thymus
Location: in the chest just above the heart and behind the sternum
Hormone: thymosins
Target: T lymphocytes
Function: stimulates development and maturation of T lymphocytes
The Adrenal Glands
Location: one above each kidney. Each gland consist of an inner adrenal medulla and outer adrenal cortex
The Adrenal Medulla
Hormone: adrenaline, noradrenaline
Target: most tissues
Function: - adrenaline: helps prepare the body doe reaction to a threatening situation, that is, it is concerned with fight-or-flight responses
- noradrenaline: increase the rate and force of the heartbeat
The Adrenal Cortex
Hormone: corticosteroids (20), main ones aldosterone and cortisol
Target: kidney, most cells
Function: - aldosterone: increases reabsorption of sodium ions and excretion of potassium ions
- cortisol: promotes normal metabolism, helps the body deal with stress, promotes repair of damaged tissues
The Pancreas
Location: just below the stomach and alongside the duodenum
Hormone: insulin, glucagon
Target: most cells, liver and fat storage tissues
Function: - insulin: stimulates uptake of glucose, lowers blood glucose level
- glucagon: stimulates break down of glycogen and fat, increases blood glucose level
The Testes
Location: male reproductive system
Hormone: androgens
Target: testes, muscles, bones
Function: stimulates sperm production, growth of muscles and skeleton, secondary sexual characteristics
The Ovaries
Location: internal female reproductive system
Hormone: oestrogen, progesterone
Target: uterus, ovaries, breast tissue
Function: - oestrogen: stimulate development of secondary sexual characteristics, regulate the menstrual cycle
- progesterone: regulates menstrual cycle and pregnancy, prepares mammary glands for milk secretion
What are some tissues that are not considered endocrine glands but secrete hormones?
- the stomach and intestines secrete hormones that coordinate the exocrine glands of the digestive system
- the heart secrete a hormone that helps reduce blood pressure
- the Placenta secretes a number of hormones that help to maintain the pregnancy.
What are the hormones secreted by the anterior pituitary?
- FSH
- luteinising hormone (LH)
- GH
- thyroid stimulating hormone (TSH)
- andrenocorticotropic hormone (ATCH)
- prolactin
What hormones are secreted by the posterior pituitary?
- oxytocin
- antidiuretic hormone (ADH)
What are some ways in which hormones change the type, activities or quantities of proteins produced?
- activate certain genes in the nucleus so that a particular enzyme of structural protein is produced
- change the shape or structure of a protein so it is turned on or off
- change the rate of production of an enzyme or structural protein by changing the rate of transcription or translation during protein synthesis
What does the pituitary gland consist of?
- anterior lobe
- posterior lobe
Why is the posterior lobe not a true gland?
It does not manufacture hormones
What hormones does the posterior lobe secrete?
Oxytocin and ADH
What hormones does the anterior lobe secrete?
- FSH, LH, GH, TSH, adrenocorticotropic hormone, prolactin
How does the posterior lobe secrete hormones?
- Both hormones are produced in special nerve cells in the hypothalamus. These cells have long extensions that pass through the infundibulum to the posterior lobe.
- Hormones manufactured in these cells move down the extensions and are stored in the posterior lobe ready for release into the bloodstream.
- The release of the hormones is triggered by nerve impulses initiated in the hypothalamus and conducted along the extensions.
How does the anterior lobe secrete hormones?
- Hormones are produced and stored in the anterior lobe.
- The hypothalamus releases releasing or inhibiting factors into the bloodstream which passes through the infundibulum to the anterior lobe.
Describe the process that stimulates the release of hormones from the anterior lobe of the pituitary.
- Low levels of the hormone
- stimulate receptors in the hypothalamus.
- This triggers the release of releasing factors
- Factors travel through blood capillaries
- Acts on anterior lobe to release hormone
How do steroid hormones work?
- The hormone diffuses through the cell membrane and combines with the protein receptor inside the cell. The receptor may be on the mitochondria, other organelles or in the nucleus.
- The hormone-receptor complex activates genes controlling the formation of particular proteins.
