Fisiología Molecular: T1

Meaning of “homeo” and “stasis”

Homeo: equal

Stasis: state

What is homeostasis?

It’s a property of cells, tissues, and organisms that allows the maintenance of the stability and constancy needed to function properly. It compensates the changes in the environment by the regulation of the metabolism.

If the homeostasis is broken…

You’re not healthy

What are three strategies to avoid breaking the homestasis by different species?

• Avoidance: minimize internal variations using some behavioral escape mechanism that allows them to avoid environmental changes → example: birds migrating, bears invernating

  • temporal: hibernation

  • spatial: migration

• Regulation: an environmental disturbance triggers compensatory actions that mantain a relatively constant internal environment (“homeo”) → example: seals mantain their temperature constant with their coat despite the outside Tª

• Conformity: the internal environment of the animal changes parallel to external conditions (“poikilo”) → example: some frogs in winter stay frozen and when they melt in spring they are still alive

Differences between homeotherm and poikilotherm:

• Homeotherm (endo): physiological mechanisms to regulate their body temepratures independently from ambient temperatures

  • mantains cte internal Tª

  • narrow range of Tª

• Poikilotherm (ecto): varies Tª as a result of variation in the environmental Tª

  • cool-blooded animals

  • wide range of Tª

What are the possible sources of body heat for homeotherms?

• shivering: muscles constractions → mechanical heat to the body core

• vasoconstriction of peripheral vessels: less blood circulating → less heat loss

• brown adipose tissue: catabolized to generate heat

Process of homestasis:

1. Stimulus: change in variable (imbalance)

2. Receptor detects change

3. Input: info sent a different pathway to control center

4. Output: info sent along a different pathway to the effector

5. Response of effector: the mechanism that has an effect on the variable and produces a response. The response is monitored continuosly by the sensor, that sends info to the control center (feedback loop)

How does a negative feedback occur?

It occurs when a system’s output acts to reduce the processes that lead to the output of that system, resulting in less output. It allows systems to self-stabilize.

When do feedback loops occur?

They occur when a stimulus or change in the environment is present. The feedback loop will respond to keep systems functioning near an ideal level.

What are some examples of negative feedbacks?

• Blood pressure

• Body temperature

• Glycemia

What are the different functions that the skin performs?

• Protection: physical barrier

• Thermoregulation: sweat glands, erector pili muscles (piel de gallina → pelos que se levantan y hacen de protección)

• Camouflage

• Sensation: receptors

How does the skin mantain homeostasis?

• Thermoregulation: sweating, vasodilation/cosntriction, vellus hair

• Barrier function

• Water balance: prevents excessive water loss through evaporation

• Sensory reception: detects changes in the environment and sends signals to the brain

What should the glucose concentration in blood be? In fasting and after feeding

Fasting: 3,9mM-5,6mM

After feeding: 7,8mM

What are the two hormones that control the glycemia homeostasis? Which organ regulates them?

• Insulin: promotes the uptake of glucose from cells when the glucose level is raised.

• Glucagon: increases the blood glucose level when it has been dropped too low.

Its regulation is controlled by the pancreas

The glycemia homeostasis is a — feedback loop. How does it work?

Negative

• High blood glucose level (stimulus):

  • Receptor: pancreas

  • Control center: pancreas→ secretes insuline

  • Effector: liver (glucose → glycogen) and tissue cells

  • Response: blood glucose back to normal

• Low blood glucose level: 

  • Receptor: pancreas

  • Control center: pancreas→ secretes gluciagon

  • Effector: liver (glycogen → glucose)

  • Response: blood glucose rises back to normal

When the glycemia homeostatic system fails, what is the illnes called? + types

Diabetes:

• Type 1: the pancreas can’t produce insuline (glucose → glycogen)

• Type 2: insulin resistance, the organ effectors cant’t take all the necessary glucose, so the quantity of insuline has to be increased. On the long term, the pancreas starts to fail and can’t produce more insuline

• Gestational diabetes: pregnant women, it can increase the probability to develope type 2

What is the blood preassure’s function?

It’s so that the blood can arrive to all the body.

The heart is the receptor. It sends the signal to the bulbo raquídeo, who sends signals to the blood vessels:

• if high blood pressure:

  • cardiac rythim decresases + blood vessels dilatate → pressure will decrease

• if low blood pressure:

  • cardiac rythim increases + blood vessels contract → blood pressure will increase

Blood pressure homestasis is a — loop

Negative

Neurons may also inhibit themselves in a — feedback loop

Negative

When a neuron stimulates the effector, it also stimulates a renshaw cell (an inhibitor neuron) that will inhibite the neuron

What is a positive feedback loop?

It is when the output of the system stimulates the system in such a way as to further increase the output. It always ends with counter-signaling that supresses the original stimulus.

In most cases harmul, but sometimes it contributes to normal function

Chilbirth is a — feedback loop

+

• El fetus hace presión sobre el cuello del útero (receptor)

• La presión es la señal al cerebro

• El cerebro es el centro de control que provocará que se libere oxitocina

• La oxitocina provoca que el útero se contraiga y que haga más presión

• + presión + oxitocina

• La señal acaba cuando se da el parto

Lactation is a — feedback loop

+

• Estímulo: el bebé se amamanta

• Receptor: receptores en la piel del pecho mandan impulso al cerebro

• Centro de control: cerebro envía señal a la glándula mamaria

• Efector: glándula mamaria libera oxitocina para que se eyecte la leche

• Final: bebé deja de amamantar

La coagulación es un feedback loop —

Positivo

Cuando se rompe un vaso sanguíneo, se inicia loop donde se agregan plaquetas, que liberarán señales para que se adhieran más plaquetas hasta que el vaso esté reparado.

El ciclo menstrual es un feedback loop —

• La primera parte: feedback loop positive

• La segunda parte: feedback loop negativo

Una hemorragia provoca un feedback loop —

Positivo dañino

Si tenemos una hemorragia, se pierde sangre, por lo que baja la presión. El cuerpo entonces lo compensa aumentando el ritmo cardíaco, aumentado lel flujo de sangre para volver a recuperar la presión. Esto tiene efecto inverso, pq se pierde más sangre más rápido (loop)