Homeostasis

excretory system function

blood regulation, blood osmolarity, acid-base balance, and removal of nitrogenous wastes

kidney structure

**cortex**: outermost layer

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**medulla**: within the cortex

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**hilum**: deep slit within the corner of its medical surface

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**renal pelvis**: widest part of the ureter

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**renal artery, vein, and ureter**: enter and exit through the renal hilum

renal portal system

1. renal artery branches out, passing through the medulla, and enters the cortex as afferent arterioles.
2. The capillary tufts derived from these afferent arterioles are known as glomeruli.
3. After blood passes through the glomerulus, the efferent arterioles then form the second capillary bed.
4. These capillaries surround the Loop of Henle and are known as vasa recta

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Bowman’s capsule

cup-like structure around the glomerulus

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leads to a long tubule with many distinct areas (in order):


1. proximal convoluted tubule
2. descending and ascending limbs of the Loop of Henle
3. distal convoluted tubule
4. collecting duct

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Bladder structure

**detrusor muscle:** muscular lining that contracts through parasympathetic activity

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**internal urethral sphincter:** consists of smooth muscle and is under involuntary control

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**external urethral sphincter**: consists of skeletal muscle and is under voluntary control

osmoregulation

kidney filters blood to form urine

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3 steps: filtration, secretion, and absorption

filtration

20% of blood is filtered as fluid into Bowman’s capsule

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movement of fluid is controlled by Starling forces

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hydrostatic pressure in glomerulus >> Bowman’s space

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osmolarity of blood in Bowman’s space >> glomerulus

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movement of solute from blood to filtrate at Bowman’s capsule

secretion

nephrons secrete salts, acids, bases, and urea directly into the tubule by either active or passive transport

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movement of solute form blood to filtrate anywhere but Bowman’s capsule

reabsorption

compounds that are filtered or secreted may be taken back up for use; reabsorbs glucose, amino acids, vitamins

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movement of solutes from filtrate to blood

nephron function

1. filtrate enters the proximal convoluted tubule (PCT) where amino acids, glucose, water soluble vitamins, and salts are reabsorbed along with water; PCT is also the site for waste of H+, K+, Urea, and NH3
2. Filtrate from the PCT enter the descending limb of the Loop of Henle before entering the ascending limb of the Loop of Henle


1. descending limb is permeable to water only
2. ascending limb permeable to salts only
3. filtrate enters the distal convoluted tubule (DCT)


1. responds to aldosterone which promotes sodium reabsorption
2. site of waste production secretion
4. filtrate goes to the collecting duct


1. responsive to aldosterone and ADH

countercurrent multiplier system

flow of filtrate through the Loop of Henle is in the opposite direction from the flow of blood

blood pressure

Aldosterone, steroid hormone, is secreted by the adrenal cortex in response to decreased blood pressure → decreased blood pressure stimulates the release of **renin** from **juxtaglomerular cells** in the kidney → renin then cleaves **angiotensinogen** to form **angiotensin I → Angiotensin I** is then metabolized by **angiotensin-converting enzyme** in the lungs to form **angiotensin II** which promotes the release of aldosterone in the adrenal cortex

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**ADH**, peptide hormone, synthesized by the hypothalamus and released by the posterior pituitary in response to high blood osmolarity → directly alters the permeability of the collecting duct, allowing more water to be reabsorbed by making the cell junctions of the duct leaky

osmotic pressure

“sucking” pressure that draws water into the vasculature caused by all dissolved particles

oncotic pressure

osmotic pressure that is attributable to dissolved proteins specifically

bicarbonate buffer system

major regulator of blood pH

structure of skin

hypodermis (subcutaneous layer), dermis, and epidermis

skin (intugment)

largest organ in the body

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derived from the ectoderm

epidermis

subdivided into layers (**strata)**

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from deepest layer → outward:

* stratum basale (basal cell layer)
* stratum spinosum (squamous cell layer)
* stratum granulosum (granular cell layer)
* stratum lucidum
* stratus corneum (horny cell layer)

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stratum basale

skin layer that contains stem cells and is responsible for proliferation of **keratinocytes**

karitinocytes

predominant cell of the skin that produce **keratin**

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keratin forms fingernails and hair

stratum spinosum

layer of skin that becomes connected to each other

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site of Langerhans cells

stratum granulosum

layer of skin where keratinocytes die and lose there nuclei

stratum lucidium

layer of skin that is only present in thick, hairless skin such as the skin on the sole of the foot or palms; nearly transport layer

stratum corneum

layer of skin that contains up to several dozen layers of flattened keratinocytes, forming a barrier that prevents invasion by pathogens and that helps to prevent fluid or salt loss

calluses

form from excessive keratin deposition in areas of repeated strain due to friction; provide protection against damage in the future

melanocytes

cell type derived from neural crest cells and found in the stratum basale

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produce **melanin,** pigment that serves to protect skin from DNA damage caused by UV radiation. Once produced, the pigment is transferred to the keratinocytes

Langerhans cells

special macrophages that reside within the stratum spinosum that are capable of presenting antigens to to T-cells in order to activate the immune system

layers of the dermis

**papillary layer:** upper layer

**reticular layer:** consists of loose connective tissue

**reticular later:**

dermis

sweat glands, blood vessels, and fair follicles originate here

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most sensor receptors are also located here

Merkel cells

sensory receptors found at the epidermal-dermal junction

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connected to sensory neurons and are responsible for deep pressure and texture sensation within the skin

Meissner’s corpuscles

respond to light touch

Ruffini endings

respond to stretch

Pacinian corpuscles

respond to deep pressure and vibration

hypodermis

layer of connective tissue that connected the skin to the rest of the body

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contains fat and fibrous tissue

skin thermoregulation

**sweating** is controlled by autonomic nervous system

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arrector pili cause hairs on the skin to stand up to help catch heated air near the skin

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**shivering:** skeletal muscle may begin to contract rapidly

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**white fat and brown fat:** layer of fat below the skin

sweating mechanism

body temperatures rise above the set point determined by the hypothalamus → postganglionic sympathetic neurons that utilize acetylcholine innervate sweat glands and promote the secretion of water with certain ions onto the skin → heat is then absorbed from the body as the water molecules undergo a phase change to evaporate

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at the same time:

arteriolar vasodilation occurs to maximize heat loss

piloerection mechanism

arterioles that feed the capillaries of the skin constrict, limiting the quantity of blood reaching the skin

shivering mechanism

skeletal muscles contract rapidly; requires a sizable amount of ATP that is converted to thermal energy

white fat

layer of fat just below the skin that helps insulate the body

brown fat

present in infants

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has a much less efficient electron transport chain which means that more heat energy is released as fuel is burned