Chapter 31 Biology: Homeostasis (Part 2)

homeostasis

• the maintaining of a relatively constant or stable internal environment

how is body temperature regul;ated?

the portion of the brain called hypothalamus detects changes

what happens when the temperature of blood is above 37C

1. neurons in the hypothalamus detect the change

2. hypothalamus gets you to sweat and dilate the superficial blood vessels

what happens when the temperature of blood is below 37C?

1. neurons in the hypothalamus detect the change

2. hypothalamus gets you to shiver and constrict superficial blood vessels

endothermic

• mammals and birds

• warm blooded

• can maintain a relatively constant internal temperature independent of the environmental temperature

ectothermic

• vertebrates other than mammals and birds

• cold blooded

• their body temperatures are dependent on the environmental temperature

how are blood glucose levels regulated?

the pancreas (an endocrine gland) produces the appropriate hormones (chemical signals transported by the blood)

how is high blood glucose regulated?

1. pancreas releases insulin

2. pancreas stimulates cells to take up glucose

3. lowers blood glucose

how is low blood glucose regulated?

1. pancreas releases glucagon

2. stimulates the liver to break down glycogen (a polysaccharide)

3. raises blood glucose

how is glucagon stored?

• generously stores in liver

• some stores in skeletal muscle to be used in emergencies to move

osmoregulation

• the balancing of water and salts in the body

• maintains homeostasis so cells don’t lyse or shrivel

osmoregulatory system

removes metabolic wastes from the body through excretion

what happens to amino acids or nucleic acids when animals catabolize them?

• they provide energy or are converted into carbohydrates or lipids

• produce nitrogen containing byproducts called nitrogenous wastes (coming from the amino group)

ammonia

• NH₃

• toxic

• produced by most fishes and tadpoles

• are eliminated through the gills and excretion of a dilute urine to make the ammonia less toxic

• easy to make but costs the most water

urea

• less toxic

• soluble in water so large amounts can be excreted in the urine

• sharks, adult amphibians, and mammals

• made in the liver

what is the pathway of urea?

• made in the liver

• carried in the bloodstream

• filtered by the kidneys

• excreted in the urine

uric acid

• slightly water soluble

• precipitates out of solution so it can be excreted using very little water

• reptiles, birds, and insects

• needed the most energy to produce

which excretory structure do flatworms use?

protonephridia— tubules with flame cells whose cilia draw fluid in, which gets filtered and expelled through excretory pores

what excretory structure do insects use?

Malpighian tubules— dump waste directly into the gut to be expelled with feces, which conserves water efficiently

what excretory structure do earthworms use?

Nephridia— tubules surrounded by a capillary network with a bladder and more to expel waste, one pair per body segment

what are the excretory organs of vertebrates?

kidneys, which contain many tubules (nephrons) that filter blood and produce urine

what is the common food across all excretory systems?

tubules filter fluid, recover what the body needs, and expel the rest as waste

kidney

• filters waste from the blood

• the waste is excreted in the urine

ureter

• tube which carries the urine from the kidney to the urinary bladder

  • within the kidney, the ureter flares open to form a funnel-like structure called the renal pelvis

urinary bladder

stores the urine

urethra

tube through which the urine passes out of the body

what is the full sequence of the urinary system in humans?

1. the blood arrives via the renal arteries, one going to each kidney, delivering blood that needs to be filtered

2. inside the kidney, the blood gets filtered through the nephrons— waste excess water, and salts get pulled out and become urine, while clean blood exits

3. the filtered blood leaves the kidneys through the renal veins, which drain into the inferior vena cava and return the blood to circulation

4. the urine produced by the kidneys moves down the uterus (one from each kidney) towards the bladder

5. the urinary bladder stores the urine until the body is ready to expel it

6. the urethra carries urine from the bladder to the outside of the body

nephrons

• the functional unit of the mammalian kidney

• located primarily in the renal cortex, but others dip down into the renal medulla

• 1 million nephrons make up the kidney

renal cortex

the outer portion of the kidney

renal medulla

the inner portion of the kidney

what are the three portions of the mammalian nephron?

• filter

• tube

• duct

nephron filter

• Bowman’s capsule (glomerular capsule)

• contains the glomerulus

glomerulus

• a tiny ball of capillaries where blood first arrives from the renal artery.

• high blood pressure forces fluid containing water, salts, glucose, urea, and other small molecules out of the blood

parents of the nephron tube

• proximal convoluted tubule

• loop of Henle

• distal convoluted tubule

what is the role of the bowman’s capsule?

a cup-shaped structure wrapped around the glomerulus that catches all of the glomerular filtrate and funnels it into the tubule

how glomerular filtration driven by blood pressure?

• blood enters the glomerulus through a high pressure vessel and a wide arteriole and exits through a narrower one, creating a bottleneck that builds up pressure.

• this pressure forces small molecules through the capillary walls into the bowman’s capsule passively

how does blood arrive at the glomerulus?

through the renal artery, which branches into smaller and smaller vessels until it reaches the glomerulus

What happens in the proximal convoluted tubule?

• Nutrients and salts are actively transported back into the peritubular capillary network

• Most of the useful substances are recovered here from the glomerular filtrate

What is the peritubular capillary network?

The capillaries surrounding the tubules that reabsorb recovered nutrients, salts, and water back into the bloodstream.

What is the Loop of Henle?

a U-shaped section of the tubule that dips deep into the inner part of the kidney (called the medulla) and back up

Why does the loop of henle dip so deep?

• The deeper it dips, the more salt it can pump out into the surrounding tissue, and the stronger the concentration gradient it can build

Why does the Loop of Henle use salt to create a concentration gradient?

• Because salt is the most abundant solute in the filtrate and is very effective at creating osmotic gradients

• wherever salt concentration is high, water is pulled toward it by osmosis

• this allows the kidney to concentrate urine without actively pumping water

What is the role of the Loop of Henle?

A U-shaped tubule that pumps salt from the filtrate into the surrounding kidney tissue, creating a concentration gradient that will later pull water out of the collecting duct by osmosis to concentrate urine for water retention

What is the role of the distal convoluted tubule?

• To fine tune the filtrate by adjusting salt levels and pH based on the body's current needs before it reaches the collecting duct

• it secretes H⁺ ions to regulate acidity, and tubular secretion here allows additional waste products and drugs to be pushed from the capillaries into the filtrate for excretion.

What is the role of the collecting duct?

To reabsorb the remaining water from the filtrate by osmosis using the concentration gradient established by the Loop of Henle, producing concentrated urine

what does urine contain at the end of the collecting duct?

• water, urea, uric acid, salts, ammonia, and creatinine- everything that was not absorbed

why is the proximal convoluted tubule described as leaky?

because it is intentionally permeable, allowing nutrients, salts, and water to pass back through its walls into the peritubular capillary network to be reabsorbed