quiz 3 (8-)

How do body parts grow to their right sizes?

• self regulate growth intrinsically inside tissues to reach a fixed size

• Regulate size using cues from the environment

• Most cases both of the above

autonomous determination of limb size

• gene control

• Size embedded in the cells very early in an animals life

• A limb grafted from another species will grow to the expected size of the donor species

Describe the mice spleen experiment

A mouse whose spleen was removed had 6 fetal mice spleens implanted. The implanted spleens grew to a proportional fraction of the size of the adult spleen, leaving the mouse with a normal total amount of spleen tissue. Implying the spleen tissue knows how much to grow based on body weight.

an experiment found that two closely related endoderm derivatives, the liver and pancreas, respond to developmental changes in progenitor cells differently. Why?

The liver exhibit regulated growth in development and robust regeneration in adulthood because they rely on extrinsic signals. The pancreas exhibit reduced regenerative capacity in adulthood because of intrinsic growth constraints that are imprinted early in adulthood.

What are different ways organs reach their target size and growth?

• limb bud transplantation in salamanders suggest a ruler mechanism intrinsic to each organ

• organs like liver and thyroid follow regulative control where final size relies on extrinsic cues mostly linked to function

• Gut, pancreas, and thymus do not adjust to recipient animal size after transplantation nor do they regrow to normal size after ablation early in development

• Muscle growth control - myostatin

• Liver growth, Hippo pathway, regulate organ size and play potential role controlling cancers

Hippo Pathway

Restrict tissue growth in adults and regulate cell proliferation, differentiation, and migration in developing organs. Dis regulation of the pathway leads to aberrant cell growth and neoplasia.

Where does the heart develop from?

Embryonic mesoderm (anterior splanchnic mesoderm)

What regulates heart and body growth?

Thyroid, growth hormone

Heart growth

• Immediately after birth cell proliferation

• during exponential growth a combination of hyperplasia and hypertrophy

• At maturation hypertrophy only

• Follows body growth (isometric)

What role does GH and thryroxine play in heart growth?

• growth can be compensated with supplementation of GH and thyroxine

• Thyroxine required to maintain mass and performance

Heart compensatory growth

• can result from exercise or exposure to high elevation

• Independent of changes in body mass

• Constant heart to body mass ratio except when blood pressure has increased (smaller in larger animals than small bc smaller animal has higher pulse rate)

• Without sufficient of this chronic overload cause cardiac failure in mature animal (why rate of heart growth is governed by blood pressure increase or decrease)

Heart and nutrition

• not appreciably influenced by changes in food consumption

• Does not change drastically with nutritional plans like body mass

Where does the kidney develop from?

Embryonic mesoderm

Kidney growth size

• weight proportional to the surface area of the body

• small species have relatively larger of this organ than large species

• Body weight and this organ have a positive linear relationship

• Renal efficiency comprised above a certain size

• Animals larger than man have multi-lobed

Why is the bovine kidney lobulated?

• embryologically they originate as distinct lobules that fuse as they grow and develop

• lobulations on external surface due to fetal lobulation

• Most animals lose fetal lobulations, bovine do not

Kidney growth

• number of nephrons fixed early in life

• Organ growth through increase in nephron size

• Malnutrition early in life can reduce the number of nephrons

• Compensatory renal hypertrophy inversely related to the animals age

• When one is removed the remaining organ becomes larger (compensatory hypertrophy)

Kidney growth and nutrition

• responded dramatically with high protein diet and increased in size

• Whatever increases its growth generally also increased work of the liver

What do the lungs develop from?

Embryonic mesoderm

lung growth

• trachio-bronchial tree forms first

• Alveoli form slowly and not all are formed at birth

• alveoli at birth are large

• number of alveoli increases early in life post natal (genetically determined) and then fixed

• later growth occurs through expansion of alveoli size, not number

• alveolar surface area is directly proportional to the rate of whole body oxygen consumption

Lung growth and body weight

• volume directly proportional to body weight

• as rate of oxygen consumption/kg body weight increases, alveolar duct diameter decreases

• animals with high oxygen demands have the smallest alveoli and hence the largest internal surface area per unit of lung volume

• structure is genetic (driven by phylogenic pressures)

What do the lungs of animals living at high altitudes look like?

more alveoli with less diameter and blood vessels in lungs

Define compensatory growth

accelerated hyperplasia and/or hypertrophy of the remaining tissue in a damaged organ to restore normal function

Compensatory pulmonary hypertrophy (pneumonectomy) in lungs 

• high altitudes

  • chronic hypoxia, animals at high altitudes exhibit greater lung volumes and pulmonary diffusing capacities

• removal of one lung

• hypertrophy 

Hyperoxia in lungs

• excess supply of O2

• reduces lung volume, alveolar surface area and alveolar numbers

What do the mouth, teeth, and salivary glands develop from?

ectoderm

What makes up the alimentary tract?

• mouth

• teeth

• salivary glands

• tongue

• stomach

• intestines

• throat

• esophagus

Where do significant post-natal developments occur in alimentary tract growth? 

stomach and intestines 

What do the tongue, stomach, and intestines develop from?

mesoderm

What do the throat, root of tongue, and esophagus develop from?

endoderm

Digestive tract growth

• growth relative to body size (isometric)

• size affected by function

• rumen increases in size with forage diet

• establishment of rumen microbial population from dam and environment

• number of intestinal villi fixed at maturity

• height of villi and depths of crypts vary with need for absorption

What can cause hypertrophy of stomach and gut? 

hyperphagia (excessive appetitie) 

What does the liver develop from?

jointly from mesoderm and endoderm

Liver growth

• size relatively constant to body mass

• size increases through cell proliferation

• grows faster than rest of the body in embryonic stage (positive allometry)

• Grows slower than rest of the body postnatally (negative allometry)

• size affected by function

• capable of hyperplasia and regeneratig its mass

• size decrease with poor nutrition

Liver and nutrition 

responds dramatically with change of nutritional plane 

Organs of digestion are related to what?

feed intake

Spleen and epidermis growth are directly proportional to what?

body size

Organ formation relies on what?

connective tissue scaffold of collagen

True or false: the size of the heart increases with the size of the body (isometric growth) 

true 

Animal organs regulate their size by taking cues fro other cells and their environment, turning growth on and off as needed. This rule applies to which organ?

liver

True or false: animals with high oxygen demands have the smallest alveoli diameters and therefore, the largest internal surface area per unit lung volume

true

True or false: when the liver is damaged, it has the ability to regenerate itself up to 90%

true

What is the general function of the endocrine system?

regulation of body functions to maintain homeostasis 

What is the reaction speed and duration of the endocrine system to stimuli?

reaction time and slow and the duration of effects are long

What is the general function of the nervous system?

regulation of body functions to maintain homeostasis

What is the reaction speed and duration of the nervous system to stimuli?

reaction is fast, and duration of effects is short 

what are the target tissues of the endocrine system? 

almost all body cells and tissues 

What are the target tissues of the nervous system?

muscle and glandular tissue

What are the chemical messenger and messenger producing cells of the endocrine system?

hormones, produced by endocrine gland cells or modified neurons 

What are the chemical messenger and messenger producing cells of the nervous system?

neurtransmitter, produced by neurons

What is the distance from chemical message in the endocrine system?

long (via bloodstream), production source to target tissue

What is the distance from chemical message in the nervous system?

short (across synaptic space)

Hormones

• produced by endocrine (ductless) glands and secrete into the bloodstream

• three classes based on their chemical structure 

  • Amino acids derived hormones

  • Protein/peptide hormones

  • Lipid derived hormones 

Amino acid derived hormones

• water soluble but insoluble in lipids

• found on the surface of the target cells

• adrenal medulla: epinephrine, norepinephrine 

• thyroid gland: thyroxine 

• pineal gland: melatonin 

• hypothalamus: dopamine  

Protein/peptide hormones

• water soluble but insoluble in lipids 

• found on the surface of the target cell

• anterior pituitary: thyroid stimulating hormone, follicle stimulating hormones, growth hormone, prolactin

• posterior pituitary: oxytocin

• pancreas: insulin, glucagon

Lipid derived hormones

• derived from cholesterol-lipid soluble hormones

• steroid hormones

  • from gonads: estradiol, testosterone, progesterone

  • from adrenal cortex: cortisol and aldosterone

What does oxytocin do?

contractions during labor and production of milk

Why are amino acids derived from hormones and protein/peptide hormones receptors found on the surface of the target cells? 

they cannot pass through the cell plasma membrane 

What is the function of growth hormone releasing hormone? (hypothalamus) 

regulates growth hormone release in the pituitary gland

What is the function of thyrotropin releasing hormone? (hypothalamus) 

regulates thyroid stimulating hormone release in the pituitary gland 

What is the function of gonadotropin releasing hormone? (hypothalamus) 

regulates LH and FSH production in the pituitary gland

What is the function of corticotropin releasing hormone? (hypothalamus) 

regulates adrenocorticotropin hormone release in the pituitary gland 

What is the function of growth hormone? (Anterior Pituitary gland)

promotes growth and influences the
metabolism of proteins, carbohydrates, and
lipids; stimulates protein synthesis

What is the function of thyroid stimulating hormone? (Anterior Pituitary gland)  

Stimulates the production and secretion of
thyroid hormones by the thyroid gland

What is the function of adrenocorticotropic hormone? (Anterior Pituitary gland)

triggers adrenal glands to release cortisol, the
stress hormone

What is the function of luteinizing hormone? (Anterior Pituitary gland)

Controls production of sex hormones
(estrogen in female and testosterone in male)
and the production of eggs in female and
sperm in male

What is the function of follicle stimulating hormone? (Anterior Pituitary gland)

Stimulates the growth of follicles in the
ovaries and induces the formation of sperm in
the testes

What is the function of prolactin? (Anterior Pituitary gland)

Initiates and maintains milk production in
udder; impacts sex hormone levels

What is the function of Antidiuretic hormone? (posterior pituitary) 

affects water retention in kidneys; controls blood pressure

What is the function of oxytocin? (Posterior pituitary)

stimulates contraction of uterus and milk ducts in the breast

What is the function of aldosterone? (adrenal cortex) 

increases blood sodium levels, regulates salt, water balance and blood pressure

What is the function of corticosteroid/cortisol (stress hormone)? (adrenal cortex) 

• anti inflammatory 

• maintains blood sugar levels, blood pressure, and muscle strength 

• regulates salt and water balance

What is the function of epinephrine? (adrenal medulla)

increases heart rate, oxygen intake, and blood flow

What is the function of norepinephrine? (adrenal medulla)

maintains blood pressure

What is the function of glucagon? (pancreas)

raises blood sugar levels

What is the function of insulin? (pancreas)

lowers blood sugar levels, stimulates metabolism of glucose, reduce metabolism of fatty acids 

What is the function of estrogen? (ovaries) 

affects development of female sexual characteristics and reproductive development, important for functioning of uterus and breasts, also protects bone health 

What is the function of progesterone? (ovaries)

Stimulates the lining of the uterus for fertilization, prepares the breasts for milk production

What is the function of testosterone? (testes)

develop and maintain male sexual characteristics and maturation 

What is the function of the parathyroid hormone? (parathyroid glands) 

• regulator of blood calcium levels 

• raises blood calcium levels by promoting intestinal calcium absorption, mobilizing calcium from bones, and enhancing kidney reabsorption of calcium 

• lowers phosphate levels by increasing its excretion through the kidneys 

What is the function of the thyroid hormone? (thyroid gland) 

• controls metabolism 

• affects growth, maturation, nervous system, activity and metabolism

What is the function of the calcitonin?

• regulates the calcium level in blood

• enhances bone calcium deposit

What is the function of melatonin? (pineal gland)

releases melatonin during night hours to help with sleep (circadian)