Dermis and Hypodermis

Dermis & Hypodermis

Characteristics of the Dermis

• Dermis is composed of dense irregular connective tissue.
• It contains nerves, blood vessels, sweat glands, and hair follicles.
• The boundary between the epidermis and the dermis is a wavy layer called the dermal papilla.
• The irregular surface of the dermal papilla causes fingerprints (or epidermal ridges).
• These ridges increase friction, allowing easier object pickup.
• The dermis has a papillary layer made of loose connective tissue.
• The reticular layer is made of bundles of collagen fibers.

Lines of Cleavage

• The arrangement of collagen fibers causes lines of cleavage or lines of tension

Importance for Surgeons

• Cuts should be made parallel to the lines of cleavage.

Blood Flow

• During exercise, blood vessels in the dermis swell, causing skin to appear red.
• Cooling the body is permitted as heat dissipates from the blood.
• Decubitus ulcers (bedsores) form when blood supply to the skin is restricted for a prolonged time.

Characteristics of the Hypodermis

• The hypodermis is also known as the subcutaneous layer.

• The hypodermis is not actually part of the skin.

• It is composed of loose fatty connective tissue that connects the skin to muscle or bone.

• The hypodermis also insulates and stores nutrients.

• The dermis is found just deep of the epidermis and contains glands and nerves.

• It has a papillary layer and a reticular layer made of collagen that forms lines of cleavage.

• The hypodermis or subcutaneous layer anchors the dermis to the underlying organs.

Skin Glands

Sudoriferous Glands

• There are 2 types of sudoriferous glands
• Eccrine: Merocrine sweat glands that aree abundant on soles, feet, and forehead.
• Appocrine: Merocrine exclusively in armpit/genitals

Eccrine Sweat Glands

• Long tubes that open into pores on the suface of the skin
• Sweat is 99% water with trace amounts of salts, vitamines, wastes and an antimicrobial peptide called dermidin.
• Sweat is generally acidic.

Apocrine vs Eccrine

• Apocrine sweat glands produce fatty subtances, proteins, and smell. They are found in armpits and genitals.
• Eccrine sweat glands produce mostly water, and have no smell. They are found on hands and feet

Sebaceous Glands Characteristics

• Sebaceous glands produce sebum (oil).

• Sebum is usually secreted onto hair and there are more oil glands on the scalp and face and none on the palms or soles of feet.

• Are holocrine glands (whole burst cells).

• Function is to lubricate skin/hair and antimicrobial/kills bacteria.

• The amount of oil produced is based on inheritance but usually increases during puberty.

• The sudoriferous glands releases sweat and some also produce fats and proteins they are merocrine glands.

• Sebaceous glands are found near hair and produce sebum (oil).

Hair & Nails

Hair functions

• Protection and warmth for the head
• Protection for the body
• Protection for eyes through eyelashes
• Protection for noise through noise hair

Hair structure

• The part of hair sticking out of the skin is called the shaft.
• Hair is protected by the outermost layer called a cuticle.
• The hair follicle is located within the dermis
• Hair cells divide within the follicle in a region called the papilla, and push out as new cells are formed
• These dead cells are continually pushed out as the hair shaft

Nails

• Nails are made of hard Keratin

• Nails have 4 basic parts:

  • Nail: produces heavily cells that become the nail body.
  • Nail is protected on slides by nail
  • Lunula ("little moon") which produces cells becomes the nail body, is whiter due to their high concentration
  • Thickness is due to high concentration which causes a color difference.

• Hair and nails provide protection while nails grow from hair cells.

Relación entre la investigación cuantitativa y cualitativa

Propósito

• Cuantitativa: Explicar, predecir, confirmar
• Cualitativa: Explorar, describir, interpretar.

Enfoque

• Cuantitativa: Estrecho, probar hipótesis específicas.
• Cualitativa: Amplio, descubrir nuevas variables/relaciones.

Naturaleza de la realidad

• Cuantitativa: Objetiva; única realidad, conocida independientemente del investigador.
• Cualitativa: Subjetiva; múltiples realidades, construidas por los participantes.

Perspectiva

• Cuantitativa: "Desde afuera"; el investigador es independiente.
• Cualitativa: "Desde adentro"; el investigador interactúa con los participantes.

Contexto

• Cuantitativa: Descontextualizada; busca generalizaciones universales.
• Cualitativa: Contextualizada; considera el entorno específico.

Variables

• Cuantitativa: Controladas, manipulación y medición de variables.
• Cualitativa: Holísticas, las variables se examinan en su complejidad natural.

Diseño

• Cuantitativa: Predefinido; estructurado y estandarizado.
• Cualitativa: Emergente; flexible y adaptable.

Muestra

• Cuantitativa: Grande; busca representatividad estadística.
• Cualitativa: Pequeña; busca profundidad y comprensión.

Recolección de datos

• Cuantitativa: Instrumentos estandarizados; encuestas, experimentos.
• Cualitativa: Entrevistas, observaciones, análisis de documentos.

Análisis de datos

• Cuantitativa: Estadístico; busca patrones y relaciones numéricas.
• Cualitativa: Interpretativo; busca significados y temas recurrentes.

Resultados

• Cuantitativa: Numéricos; tablas, gráficos, pruebas estadísticas.
• Cualitativa: Narrativos; descripciones detalladas, citas, interpretaciones.

Validez

• Cuantitativa: Confiabilidad, validez interna y externa.
• Cualitativa: Credibilidad, transferibilidad, dependencia, confirmabilidad.

Reporte

• Cuantitativa: Objetivo; estilo impersonal, lenguaje técnico.
• Cualitativa: Reflexivo; reconoce la influencia del investigador, lenguaje accesible.

Rol del investigador

• Cuantitativa: Neutral; minimiza el sesgo personal.
• Cualitativa: Activo; involucrado en la construcción del conocimiento.

Generalización

• Cuantitativa: Busca generalizar los resultados a la población.
• Cualitativa: Busca comprender la particularidad del contexto estudiado.

Uso de la teoría

• Cuantitativa: Prueba o modifica teorías existentes.
• Cualitativa: Desarrolla nuevas teorías o marcos conceptuales.

Preguntas

• Cuantitativa: Cerradas; enfocadas en la medición de variables específicas.
• Cualitativa: Abiertas; exploran perspectivas y significados.

Tipo de razonamiento

• Cuantitativa: Deductivo; de lo general a lo particular.
• Cualitativa: Inductivo; de lo particular a lo general.

Objetividad

• Cuantitativa: Busca la objetividad a través de la estandarización y el control.
• Cualitativa: Reconoce la subjetividad inherente a la investigación social.

Tipo de conocimiento

• Cuantitativa: Nomotético; busca leyes generales.
• Cualitativa: Ideográfico; busca comprender lo único y particular.

Criterios de calidad

• Cuantitativa: Rigor metodológico, validez estadística, replicabilidad.
• Cualitativa: Credibilidad, relevancia, significancia, reflexividad.

Propósito del reporte

• Cuantitativa: Comunicar hallazgos objetivos y generalizables.
• Cualitativa: Compartir comprensiones profundas y contextualizadas.

Audiencia

• Cuantitativa: Científicos, tomadores de decisiones, público en general.
• Cualitativa: Participantes, comunidades, otros investigadores.

Limitaciones

• Cuantitativa: Puede simplificar demasiado la realidad, perder detalles importantes.
• Cualitativa: Puede ser difícil generalizar los resultados, subjetividad del investigador.

Fortalezas

• Cuantitativa: Permite medir y cuantificar fenómenos, establecer relaciones causales.
• Cualitativa: Permite comprender la complejidad de los fenómenos sociales, generar hipótesis.

Prérequis Algèbre Linéaire

Ensembles

Définition

• Un ensemble est une collection d'objets.
• Ces objets sont appelés éléments de l'ensemble.

Notation

• $x \in E$: $x$ est un élément de $E$
• $x \notin E$: $x$ n'est pas un élément de $E$
• $E = {x_1, x_2,..., x_n}$: ensemble $E$ contenant les éléments $x_1, x_2,..., x_n$
• $\emptyset$: ensemble vide (ne contenant aucun élément)

Opérations sur les ensembles

• $E \cup F$: union de $E$ et $F$ (ensemble contenant tous les éléments de $E$ et de $F$)
• $E \cap F$: intersection de $E$ et $F$ (ensemble contenant les éléments communs à $E$ et $F$)
• $E \setminus F$: différence de $E$ et $F$ (ensemble contenant les éléments de $E$ qui ne sont pas dans $F$)
• $E \subseteq F$: $E$ est un sous-ensemble de $F$ (tous les éléments de $E$ sont dans $F$)

Applications

Définition

• Une application $f$ de $E$ dans $F$ est une relation qui à chaque élément de $E$ associe un unique élément de $F$.

Notation

• $f: E \rightarrow F$
• $x \mapsto f(x)$

Vocabulaire

• $E$: ensemble de départ
• $F$: ensemble d'arrivée
• $f(x)$: image de $x$ par $f$
• antécédent de $y$: élément $x$ de $E$ tel que $f(x) = y$

Propriétés

• injective: tout élément de $F$ a au plus un antécédent dans $E$
• surjective: tout élément de $F$ a au moins un antécédent dans $E$
• bijective: tout élément de $F$ a exactement un antécédent dans $E$ (injective et surjective)

Corps

Définition

• Un corps est un ensemble $K$ muni de deux opérations, l'addition et la multiplication, vérifiant les propriétés suivantes:
• $(K, +)$ est un groupe commutatif (élément neutre 0, existence d'un opposé)
• $(K \setminus {0}, \times)$ est un groupe commutatif (élément neutre 1, existence d'un inverse)
• La multiplication est distributive par rapport à l'addition: $\forall x, y, z \in K, x \times (y + z) = x \times y + x \times z$

Exemples

• $\mathbb{R}$: ensemble des nombres réels
• $\mathbb{C}$: ensemble des nombres complexes
• $\mathbb{Q}$: ensemble des nombres rationnels

Polynômes

Définition

• Un polynôme à coefficients dans un corps $K$ est une expression de la forme:

$P(X) = a_0 + a_1X + a_2X^2 +... + a_nX^n$

où $a_0, a_1,..., a_n \in K$ et $X$ est une indéterminée.

Vocabulaire

• $a_i$: coefficients du polynôme
• $n$: degré du polynôme (si $a_n \neq 0$)
• $a_nX^n$: terme dominant

Opérations sur les polynômes

• Addition: $(P + Q)(X) = P(X) + Q(X)$
• Multiplication: $(P \times Q)(X) = P(X) \times Q(X)$
• Composition: $(P \circ Q)(X) = P(Q(X))$

Racine d'un polynôme

• $\alpha \in K$ est une racine de $P$ si $P(\alpha) = 0$

Factorisation

• Tout polynôme de degré $n$ à coefficients dans $\mathbb{C}$ admet $n$ racines (comptées avec multiplicité).

Chemical Kinetics

Reaction Rate

• Chemical kinetics studies reaction rates, how they change, and reaction mechanisms.
• Consider the reaction: $aA + bB \longrightarrow cC + dD$ where a, b, c, d are stoichiometric coefficients.
• Rate can be expressed in terms of reactants disappearing or products appearing: Rate $= -\frac{1}{a}\frac{d[A]}{dt} = -\frac{1}{b}\frac{d[B]}{dt} = \frac{1}{c}\frac{d[C]}{dt} = \frac{1}{d}\frac{d[D]}{dt}$
  • Reactant concentration decreases with time, indicated by '-'.
  • Product concentration increases with time, indicated by '+'.
  • Rate is always positive.

Factors Affecting Reaction Rate

• Concentration of Reactants: Higher concentration, faster rate.
• Temperature: Higher temperature, faster rate.
• Surface Area of a Solid Reactant: Higher surface area, faster rate.
• Pressure of Gaseous Reactants or Products: Higher pressure, faster rate.
• Presence of a Catalyst: Catalyst speeds up the reaction.
• Nature of Reactants: Some reactions are naturally faster than others.
• Radiation: Radiation increases the rate of certain reactions.

Rate Law

• Expresses rate as a function of reactants' concentrations.
• For $aA + bB \longrightarrow cC + dD$, Rate $= k[A]^x[B]^y$.
• k is the rate constant. x is the order with respect to A. y is the order with respect to B. (x + y) is the overall order.
  • Exponents x and y are experimentally determined and not necessarily equal to stoichiometric coefficients.

Types of Reaction Rates

• Instantaneous Rate: The rate at a specific point in time.
• Initial Rate: The instantaneous rate at $t = 0$.
• Average Rate: The change in concentration over a period of time.

Integrated Rate Laws

• Mathematical expressions that describe the change in concentration of a reactant as a function of time, derived from differential rate laws.

Zero-Order Reactions

• For the reaction $A \longrightarrow Products$, Rate $= k$.
• Integrated Rate Law: $[A]_t = -kt + [A]_0$
  • $[A]_t$ is the concentration of A at time t.
  • $[A]_0$ is the initial concentration of A.
  • k is the rate constant.
• Half-Life: $t_{1/2} = \frac{[A]_0}{2k}$
  • Plotting $[A]_t$ vs. $t$ yields a straight line (slope = $-k$, y-intercept = $[A]_0$).

First-Order Reactions

• For the reaction $A \longrightarrow Products$, Rate $= k[A]$.
• $ln[A]_t = -kt + ln[A]_0$ or $ln\frac{[A]_t}{[A]_0} = -kt$ or $[A]_t = [A]_0 e^{-kt}$
  • plotting $ln[A]_t$ vs. $t$ yields a straight line (slope = $-k$, y-intercept = $ln[A]_0$).
• Half-Life: $t_{1/2} = \frac{0.693}{k}$
  • Half-life is independent of the initial concentration.

Second-Order Reactions

• For the reaction $A \longrightarrow Products$, Rate $= k[A]^2$
• Integrated Rate Law: $\frac{1}{[A]_t} = kt + \frac{1}{[A]_0}$
• Half-Life: $t_{1/2} = \frac{1}{k[A]_0}$
  • Half-life depends on the initial concentration.
  • Plotting $\frac{1}{[A]_t}$ vs. $t$ yields a straight line (slope = $k$, y-intercept = $\frac{1}{[A]_0}$)

Collision Theory

• Reactions occur when molecules collide with enough energy and proper orientation.

Activation Energy

• Activation energy ($E_a$) is the minimum energy required for a reaction to occur.

Factors Affecting Collision Frequency

• Concentration: Higher concentration leads to more collisions.
• Temperature: Higher temperature increases molecular speed and collision frequency.
• Physical State: Gases have higher collision frequencies than liquids or solids.

Arrhenius Equation

• Describes the relationship between the rate constant, activation energy, and temperature.
• $k = A e^{-E_a/RT}$
  • Taking the natural logarithm: $ln \ k = ln \ A - \frac{E_a}{RT}$
  • Slope $= -\frac{E_a}{R}$, y-intercept $= ln \ A$ when plotting $ln \ k$ vs. $\frac{1}{T}$
• Two-Point Form: $ln \frac{k_2}{k_1} = \frac{E_a}{R} (\frac{1}{T_1} - \frac{1}{T_2})$

Determining $E_a$ Graphically

Plot $ln \ k$ vs. $\frac{1}{T}$ to obtain a straight line:

• Slope $= -\frac{E_a}{R}$
• Y-intercept $= ln \ A$

Reaction Mechanisms

• A step-by-step sequence of elementary reactions by which overall chemical change occurs.

Elementary Reactions

• Single-step reactions. Rate law can be written directly from the stoichiometry.

Molecularity

• The number of reactant molecules involved in an elementary reaction.

1. Unimolecular
2. Bimolecular
3. Termolecular

Rate-Determining Step

• The slowest step in a reaction mechanism that determines the overall rate of the reaction.

Intermediates

• A species formed in one step and consumed in a subsequent step and does not appear in the overall balanced equation

Catalyst

• A substance that speeds up a reaction without being consumed

Homogeneous Catalyst

• A homogeneous catalyst is in the same phase as the reactants.

Heterogeneous Catalyst

• A heterogeneous catalyst is in a different phase from the reactants.

Catalysis

In catalysis, the rate of a chemical reaction is increased by adding a substance known as a catalyst, which is not consumed in the catalyzed reaction and can continue to act repeatedly.

Homogeneous Catalysis

• Both the catalyst and reactants are in solution. The catalyst and reactants are in the same phase.

Example

Acid catalysis: $H^+(aq) + S(aq) \rightleftharpoons SH^+(aq)$

Heterogeneous Catalysis

• The catalyst is a solid, and the reactants are gases or liquids and are in a different phase from the reactants.

Steps

1. Adsorption
2. Diffusion
3. Reaction
4. Desorption

Examples:

• Hydrogenation of ethene on a nickel surface.
• Catalytic converters in automobiles.

Enzymes

Enzymes are biological catalysts that speed up biochemical reactions in living organisms. Typically enzymes are proteins that have specific three-dimensional structures.

Mechanism of Enzyme Action

1. Substrate Binding: $E + S \rightleftharpoons ES$ The substrate(s) binds to the active site of the enzyme, forming an enzyme-substrate complex (ES).
2. Catalysis: $ES \longrightarrow E + P$ The enzyme facilitates the reaction, converting the substrate into product(s).
3. Product Release The product(s) is/are released, and the enzyme is free to catalyze another reaction.

Michaelis-Menten Kinetics

The Michaelis-Menten equation describes the rate of enzyme-catalyzed reactions:

$V = \frac{V_{max}[S]}{K_M + [S]}$

$V$ is the reaction rate.

$V_{max}$ is the maximum reaction rate.

$[S]$ is the substrate concentration.

$K_M$ is the Michaelis constant (substrate concentration at which the reaction rate is half of $V_{max}$)

Factors Affecting Enzyme Activity

1. Temperature: Enzymes have an optimum temperature range.
2. pH: Enzymes have an optimum pH range.
3. Substrate Concentration: Reaction rate increases with substrate concentration up to $V_{max}$.
4. Inhibitors: Substances that decrease enzyme activity.

Enzyme Inhibition

Enzyme inhibitors are substances that reduce the activity of enzymes. There are several types of enzyme inhibition:

1. Competitive Inhibition: $E + I \rightleftharpoons EI$; $V = \frac{V_{max}[S]}{K_M(1 + [I]/K_I) + [S]}$
2. Noncompetitive Inhibition: $E + I \rightleftharpoons EI$; $ES + I \rightleftharpoons ESI$; $V = \frac{V_{max}[S]}{(K_M + [S])(1 + [I]/K_I)}$
3. Uncompetitive Inhibition: $ES + I \rightleftharpoons ESI$; $V = \frac{V_{max}[S]}{K_M + [S](1 + [I]/K_I)}$